diff --git a/ClosedXML/Excel/AutoFilters/XLAutoFilter.cs b/ClosedXML/Excel/AutoFilters/XLAutoFilter.cs
index 3e33697..ec79a5c 100644
--- a/ClosedXML/Excel/AutoFilters/XLAutoFilter.cs
+++ b/ClosedXML/Excel/AutoFilters/XLAutoFilter.cs
@@ -116,62 +116,59 @@
             SortColumn = columnToSortBy;
 
             // Recalculate shown / hidden rows
-            if (Enabled)
+            using (var rows = Range.Rows(2, Range.RowCount()))
             {
-                using (var rows = Range.Rows(2, Range.RowCount()))
-                {
-                    foreach (IXLRangeRow row in rows)
-                        row.WorksheetRow().Unhide();
-                }
+                foreach (IXLRangeRow row in rows)
+                    row.WorksheetRow().Unhide();
+            }
 
-                foreach (var kp in Filters)
+            foreach (var kp in Filters)
+            {
+                Boolean firstFilter = true;
+                foreach (XLFilter filter in kp.Value)
                 {
-                    Boolean firstFilter = true;
-                    foreach (XLFilter filter in kp.Value)
+                    var condition = filter.Condition;
+                    var isText = filter.Value is String;
+                    var isDateTime = filter.Value is DateTime;
+
+                    using (var rows = Range.Rows(2, Range.RowCount()))
                     {
-                        var condition = filter.Condition;
-                        var isText = filter.Value is String;
-                        var isDateTime = filter.Value is DateTime;
-
-                        using (var rows = Range.Rows(2, Range.RowCount()))
+                        foreach (IXLRangeRow row in rows)
                         {
-                            foreach (IXLRangeRow row in rows)
+                            //TODO : clean up filter matching - it's done in different place
+                            Boolean match;
+
+                            if (isText)
+                                match = condition(row.Cell(kp.Key).GetFormattedString());
+                            else if (isDateTime)
+                                match = row.Cell(kp.Key).DataType == XLDataType.DateTime && condition(row.Cell(kp.Key).GetDateTime());
+                            else
+                                match = row.Cell(kp.Key).DataType == XLDataType.Number && condition(row.Cell(kp.Key).GetDouble());
+
+                            if (firstFilter)
                             {
-                                //TODO : clean up filter matching - it's done in different place
-                                Boolean match;
-
-                                if (isText)
-                                    match = condition(row.Cell(kp.Key).GetFormattedString());
-                                else if (isDateTime)
-                                    match = row.Cell(kp.Key).DataType == XLDataType.DateTime && condition(row.Cell(kp.Key).GetDateTime());
+                                if (match)
+                                    row.WorksheetRow().Unhide();
                                 else
-                                    match = row.Cell(kp.Key).DataType == XLDataType.Number && condition(row.Cell(kp.Key).GetDouble());
-
-                                if (firstFilter)
-                                {
-                                    if (match)
-                                        row.WorksheetRow().Unhide();
-                                    else
-                                        row.WorksheetRow().Hide();
-                                }
-                                else
-                                {
-                                    if (filter.Connector == XLConnector.And)
-                                    {
-                                        if (!row.WorksheetRow().IsHidden)
-                                        {
-                                            if (match)
-                                                row.WorksheetRow().Unhide();
-                                            else
-                                                row.WorksheetRow().Hide();
-                                        }
-                                    }
-                                    else if (match)
-                                        row.WorksheetRow().Unhide();
-                                }
+                                    row.WorksheetRow().Hide();
                             }
-                            firstFilter = false;
+                            else
+                            {
+                                if (filter.Connector == XLConnector.And)
+                                {
+                                    if (!row.WorksheetRow().IsHidden)
+                                    {
+                                        if (match)
+                                            row.WorksheetRow().Unhide();
+                                        else
+                                            row.WorksheetRow().Hide();
+                                    }
+                                }
+                                else if (match)
+                                    row.WorksheetRow().Unhide();
+                            }
                         }
+                        firstFilter = false;
                     }
                 }
             }
diff --git a/ClosedXML/Excel/CalcEngine/Functions/Tally.cs b/ClosedXML/Excel/CalcEngine/Functions/Tally.cs
index 93abf67..cd6b4d5 100644
--- a/ClosedXML/Excel/CalcEngine/Functions/Tally.cs
+++ b/ClosedXML/Excel/CalcEngine/Functions/Tally.cs
@@ -89,7 +89,7 @@
             {
                 double tmp;
                 var vEnumerable = value as IEnumerable;
-                if (vEnumerable == null)
+                if (vEnumerable == null || vEnumerable is string)
                 {
                     if (TryParseToDouble(value, out tmp))
                         yield return tmp;
@@ -100,7 +100,6 @@
                     {
                         if (TryParseToDouble(v, out tmp))
                             yield return tmp;
-                        break;
                     }
                 }
             }
diff --git a/ClosedXML/Excel/CalcEngine/Functions/XLMath.cs b/ClosedXML/Excel/CalcEngine/Functions/XLMath.cs
index 4354e04..081df15 100644
--- a/ClosedXML/Excel/CalcEngine/Functions/XLMath.cs
+++ b/ClosedXML/Excel/CalcEngine/Functions/XLMath.cs
@@ -91,11 +91,11 @@
 
         public static Boolean IsEven(Int32 value)
         {
-            return Math.Abs(value % 2) < XLHelper.Epsilon;
+            return Math.Abs(value % 2) == 0;
         }
         public static Boolean IsOdd(Int32 value)
         {
-            return Math.Abs(value % 2) > XLHelper.Epsilon;
+            return Math.Abs(value % 2) != 0;
         }
 
         public static string ToRoman(int number)
diff --git a/ClosedXML/Excel/Cells/XLCell.cs b/ClosedXML/Excel/Cells/XLCell.cs
index e11eaee..30fca92 100644
--- a/ClosedXML/Excel/Cells/XLCell.cs
+++ b/ClosedXML/Excel/Cells/XLCell.cs
@@ -933,7 +933,7 @@
                     _richText = null;
                 }
 
-                if (_cellValue.Length > 0)
+                if (!string.IsNullOrEmpty(_cellValue))
                 {
                     if (value == XLDataType.Boolean)
                     {
@@ -1628,8 +1628,8 @@
                     var cell = cells.First();
                     var field = table.Fields.First(f => f.Column.ColumnNumber() == cell.WorksheetColumn().ColumnNumber());
                     field.TotalsRowFunction = XLTotalsRowFunction.None;
-                    field.TotalsRowLabel = value.ToString();
-                    this._cellValue = value.ToString();
+                    _cellValue = value.ToString();
+                    field.TotalsRowLabel = _cellValue;
                     this.DataType = XLDataType.Text;
                     return true;
                 }
diff --git a/ClosedXML/Excel/ConditionalFormats/Save/XLCFCellIsConverter.cs b/ClosedXML/Excel/ConditionalFormats/Save/XLCFCellIsConverter.cs
index d846ce3..dfad5bc 100644
--- a/ClosedXML/Excel/ConditionalFormats/Save/XLCFCellIsConverter.cs
+++ b/ClosedXML/Excel/ConditionalFormats/Save/XLCFCellIsConverter.cs
@@ -16,11 +16,7 @@
 
             conditionalFormattingRule.Operator = cf.Operator.ToOpenXml();
 
-            var formula = new Formula();
-            if (cf.Operator == XLCFOperator.Equal || cf.Operator == XLCFOperator.NotEqual)
-                formula.Text = val;
-            else
-                formula.Text = val;
+            var formula = new Formula(val);
             conditionalFormattingRule.Append(formula);
 
             if (cf.Operator == XLCFOperator.Between || cf.Operator == XLCFOperator.NotBetween)
diff --git a/ClosedXML/Excel/DataValidation/IXLDataValidation.cs b/ClosedXML/Excel/DataValidation/IXLDataValidation.cs
index 1c7b9fd..0d87c3c 100644
--- a/ClosedXML/Excel/DataValidation/IXLDataValidation.cs
+++ b/ClosedXML/Excel/DataValidation/IXLDataValidation.cs
@@ -5,7 +5,7 @@
     public enum XLErrorStyle { Stop, Warning, Information }
     public enum XLAllowedValues { AnyValue, WholeNumber, Decimal, Date, Time, TextLength, List, Custom }
     public enum XLOperator { EqualTo, NotEqualTo, GreaterThan, LessThan, EqualOrGreaterThan, EqualOrLessThan, Between, NotBetween }
-    public interface IXLDataValidation
+    public interface IXLDataValidation : IDisposable
     {
         IXLRanges Ranges { get; set; }
         //void Delete();
diff --git a/ClosedXML/Excel/DataValidation/IXLDataValidations.cs b/ClosedXML/Excel/DataValidation/IXLDataValidations.cs
index 9dfca5f..dccd8d1 100644
--- a/ClosedXML/Excel/DataValidation/IXLDataValidations.cs
+++ b/ClosedXML/Excel/DataValidation/IXLDataValidations.cs
@@ -3,7 +3,7 @@
 
 namespace ClosedXML.Excel
 {
-    public interface IXLDataValidations: IEnumerable<IXLDataValidation>
+    public interface IXLDataValidations: IEnumerable<IXLDataValidation>, IDisposable
     {
         void Add(IXLDataValidation dataValidation);
         Boolean ContainsSingle(IXLRange range);
diff --git a/ClosedXML/Excel/DataValidation/XLDataValidation.cs b/ClosedXML/Excel/DataValidation/XLDataValidation.cs
index 3ee5896..9d5ec8b 100644
--- a/ClosedXML/Excel/DataValidation/XLDataValidation.cs
+++ b/ClosedXML/Excel/DataValidation/XLDataValidation.cs
@@ -197,5 +197,10 @@
         {
             Initialize();
         }
+
+        public void Dispose()
+        {
+            Ranges?.Dispose();
+        }
     }
 }
diff --git a/ClosedXML/Excel/DataValidation/XLDataValidations.cs b/ClosedXML/Excel/DataValidation/XLDataValidations.cs
index fa339f6..3387588 100644
--- a/ClosedXML/Excel/DataValidation/XLDataValidations.cs
+++ b/ClosedXML/Excel/DataValidation/XLDataValidations.cs
@@ -50,5 +50,10 @@
         {
             _dataValidations.RemoveAll(dv => dv.Ranges.Contains(range));
         }
+
+        public void Dispose()
+        {
+            _dataValidations.ForEach(dv => dv.Dispose());
+        }
     }
 }
diff --git a/ClosedXML/Excel/Drawings/XLPicture.cs b/ClosedXML/Excel/Drawings/XLPicture.cs
index b1e44e8..d0732db 100644
--- a/ClosedXML/Excel/Drawings/XLPicture.cs
+++ b/ClosedXML/Excel/Drawings/XLPicture.cs
@@ -333,12 +333,12 @@
 
         internal void SetName(string value)
         {
-            if (value.IndexOfAny(InvalidNameChars.ToCharArray()) != -1)
-                throw new ArgumentException($"Picture names cannot contain any of the following characters: {InvalidNameChars}");
-
             if (String.IsNullOrWhiteSpace(value))
                 throw new ArgumentException("Picture names cannot be empty");
 
+            if (value.IndexOfAny(InvalidNameChars.ToCharArray()) != -1)
+                throw new ArgumentException($"Picture names cannot contain any of the following characters: {InvalidNameChars}");
+
             if (value.Length > 31)
                 throw new ArgumentException("Picture names cannot be more than 31 characters");
 
diff --git a/ClosedXML/Excel/Ranges/XLRange.cs b/ClosedXML/Excel/Ranges/XLRange.cs
index a133105..4f5f4d2 100644
--- a/ClosedXML/Excel/Ranges/XLRange.cs
+++ b/ClosedXML/Excel/Ranges/XLRange.cs
@@ -804,7 +804,9 @@
 
         public override bool Equals(object obj)
         {
-            var other = (XLRange)obj;
+            var other = obj as XLRange;
+            if (other == null)
+                return false;
             return RangeAddress.Equals(other.RangeAddress)
                    && Worksheet.Equals(other.Worksheet);
         }
diff --git a/ClosedXML/Excel/Ranges/XLRangeAddress.cs b/ClosedXML/Excel/Ranges/XLRangeAddress.cs
index d900347..2594558 100644
--- a/ClosedXML/Excel/Ranges/XLRangeAddress.cs
+++ b/ClosedXML/Excel/Ranges/XLRangeAddress.cs
@@ -191,7 +191,9 @@
 
         public override bool Equals(object obj)
         {
-            var other = (XLRangeAddress)obj;
+            var other = obj as XLRangeAddress;
+            if (other == null)
+                return false;
             return Worksheet.Equals(other.Worksheet)
                    && FirstAddress.Equals(other.FirstAddress)
                    && LastAddress.Equals(other.LastAddress);
diff --git a/ClosedXML/Excel/Ranges/XLRanges.cs b/ClosedXML/Excel/Ranges/XLRanges.cs
index 3b0650e..63c5458 100644
--- a/ClosedXML/Excel/Ranges/XLRanges.cs
+++ b/ClosedXML/Excel/Ranges/XLRanges.cs
@@ -220,8 +220,9 @@
 
         public override bool Equals(object obj)
         {
-            var other = (XLRanges)obj;
-
+            var other = obj as XLRanges;
+            if (other == null)
+                return false;
             return _ranges.Count == other._ranges.Count &&
                    _ranges.Select(thisRange => Enumerable.Contains(other._ranges, thisRange)).All(foundOne => foundOne);
         }
diff --git a/ClosedXML/Excel/Rows/XLRow.cs b/ClosedXML/Excel/Rows/XLRow.cs
index 697801e..2e660e0 100644
--- a/ClosedXML/Excel/Rows/XLRow.cs
+++ b/ClosedXML/Excel/Rows/XLRow.cs
@@ -336,7 +336,7 @@
                         else
                         {
                             Double rotation;
-                            if (textRotation == 90 || textRotation == 180 || textRotation == 255)
+                            if (textRotation == 90 || textRotation == 180)
                                 rotation = 90;
                             else
                                 rotation = textRotation % 90;
diff --git a/ClosedXML/Excel/Tables/IXLTableField.cs b/ClosedXML/Excel/Tables/IXLTableField.cs
index 4c2fb00..9fb10ec 100644
--- a/ClosedXML/Excel/Tables/IXLTableField.cs
+++ b/ClosedXML/Excel/Tables/IXLTableField.cs
@@ -16,7 +16,7 @@
         Custom
     }
 
-    public interface IXLTableField
+    public interface IXLTableField : IDisposable
     {
         /// <summary>
         /// Gets the corresponding column for this table field.
diff --git a/ClosedXML/Excel/Tables/XLTable.cs b/ClosedXML/Excel/Tables/XLTable.cs
index 4c70fc1..6eb0a9e 100644
--- a/ClosedXML/Excel/Tables/XLTable.cs
+++ b/ClosedXML/Excel/Tables/XLTable.cs
@@ -564,6 +564,8 @@
             if (AutoFilter != null)
                 AutoFilter.Dispose();
 
+            Fields?.ForEach(field => field.Dispose());
+
             base.Dispose();
         }
 
diff --git a/ClosedXML/Excel/Tables/XLTableField.cs b/ClosedXML/Excel/Tables/XLTableField.cs
index 0a975dd..c7b2bbf 100644
--- a/ClosedXML/Excel/Tables/XLTableField.cs
+++ b/ClosedXML/Excel/Tables/XLTableField.cs
@@ -213,5 +213,10 @@
                 }
             }
         }
+
+        public void Dispose()
+        {
+            _column.Dispose();
+        }
     }
 }
diff --git a/ClosedXML/Excel/XLWorkbook_Load.cs b/ClosedXML/Excel/XLWorkbook_Load.cs
index 7aa868f..fa2079c 100644
--- a/ClosedXML/Excel/XLWorkbook_Load.cs
+++ b/ClosedXML/Excel/XLWorkbook_Load.cs
@@ -278,7 +278,7 @@
                     var dTable = tableDefinitionPart.Table;
 
                     String reference = dTable.Reference.Value;
-                    String tableName = dTable?.Name ?? dTable.DisplayName ?? string.Empty;
+                    String tableName = dTable.Name ?? dTable.DisplayName ?? string.Empty;
                     if (String.IsNullOrWhiteSpace(tableName))
                         throw new InvalidDataException("The table name is missing.");
 
@@ -324,7 +324,7 @@
                     if (dTable.AutoFilter != null)
                     {
                         xlTable.ShowAutoFilter = true;
-                        LoadAutoFilterColumns(dTable.AutoFilter, (xlTable as XLTable).AutoFilter);
+                        LoadAutoFilterColumns(dTable.AutoFilter, xlTable.AutoFilter);
                     }
                     else
                         xlTable.ShowAutoFilter = false;
@@ -374,7 +374,7 @@
                         // find cell by reference
                         var cell = ws.Cell(c.Reference);
 
-                        XLComment xlComment = cell.Comment as XLComment;
+                        var xlComment = cell.Comment;
                         xlComment.Author = authors[(int)c.AuthorId.Value].InnerText;
                         //xlComment.ShapeId = (Int32)c.ShapeId.Value;
                         //ShapeIdManager.Add(xlComment.ShapeId);
@@ -384,7 +384,7 @@
                         {
                             var runProperties = run.RunProperties;
                             String text = run.Text.InnerText.FixNewLines();
-                            var rt = cell.Comment.AddText(text);
+                            var rt = xlComment.AddText(text);
                             LoadFont(runProperties, rt);
                         }
 
@@ -908,7 +908,7 @@
                 xdoc = XDocumentExtensions.Load(vmlPart.GetStream(FileMode.Open));
 
                 //Probe for comments
-                if (xdoc.Root == null) continue;
+                if (xdoc?.Root == null) continue;
                 var shape = GetCommentShape(xdoc);
                 if (shape != null) break;
             }
@@ -1361,12 +1361,9 @@
                 else
                     formula = cell.CellFormula.Text;
 
-                if (cell.CellFormula.Reference != null)
-                {
-                    // Parent cell of shared formulas
-                    // Child cells will use this shared index to set its R1C1 style formula
-                    xlCell.FormulaReference = ws.Range(cell.CellFormula.Reference.Value).RangeAddress;
-                }
+                // Parent cell of shared formulas
+                // Child cells will use this shared index to set its R1C1 style formula
+                xlCell.FormulaReference = ws.Range(cell.CellFormula.Reference.Value).RangeAddress;
 
                 xlCell.FormulaA1 = formula;
                 sharedFormulasR1C1.Add(cell.CellFormula.SharedIndex.Value, xlCell.FormulaR1C1);
@@ -2144,7 +2141,7 @@
                     if (conditionalFormat.ConditionalFormatType == XLConditionalFormatType.CellIs && fr.Operator != null)
                         conditionalFormat.Operator = fr.Operator.Value.ToClosedXml();
 
-                    if (fr.Text != null && !String.IsNullOrWhiteSpace(fr.Text))
+                    if (!String.IsNullOrWhiteSpace(fr.Text))
                         conditionalFormat.Values.Add(GetFormula(fr.Text.Value));
 
                     if (conditionalFormat.ConditionalFormatType == XLConditionalFormatType.Top10)
diff --git a/ClosedXML/Excel/XLWorkbook_Save.cs b/ClosedXML/Excel/XLWorkbook_Save.cs
index 6bc0f59..66221b7 100644
--- a/ClosedXML/Excel/XLWorkbook_Save.cs
+++ b/ClosedXML/Excel/XLWorkbook_Save.cs
@@ -1069,6 +1069,9 @@
                     {
                         if (c.HasArrayFormula)
                         {
+                            if (c.FormulaReference == null)
+                                c.FormulaReference = c.AsRange().RangeAddress;
+
                             if (c.FormulaReference.FirstAddress.Equals(c.Address))
                             {
                                 var cc = new CalculationCell
@@ -1077,9 +1080,6 @@
                                     SheetId = worksheet.SheetId
                                 };
 
-                                if (c.FormulaReference == null)
-                                    c.FormulaReference = c.AsRange().RangeAddress;
-
                                 cc.Array = true;
                                 calculationChain.AppendChild(cc);
 
@@ -2498,8 +2498,9 @@
                         if (labelOrFilterField != null && labelOrFilterField.Collapsed)
                             item.HideDetails = BooleanValue.FromBoolean(false);
 
-                        if (labelOrFilterField.SelectedValues.Count > 1
-                                 && !labelOrFilterField.SelectedValues.Contains(value))
+                        if (labelOrFilterField != null &&
+                            labelOrFilterField.SelectedValues.Count > 1 &&
+                            !labelOrFilterField.SelectedValues.Contains(value))
                             item.Hidden = BooleanValue.FromBoolean(true);
 
                         fieldItems.AppendChild(item);
diff --git a/ClosedXML/Excel/XLWorksheet.cs b/ClosedXML/Excel/XLWorksheet.cs
index 839b5d8..cdd2d65 100644
--- a/ClosedXML/Excel/XLWorksheet.cs
+++ b/ClosedXML/Excel/XLWorksheet.cs
@@ -170,13 +170,13 @@
             get { return _name; }
             set
             {
+                if (String.IsNullOrWhiteSpace(value))
+                    throw new ArgumentException("Worksheet names cannot be empty");
+
                 if (value.IndexOfAny(InvalidNameChars.ToCharArray()) != -1)
                     throw new ArgumentException("Worksheet names cannot contain any of the following characters: " +
                                                 InvalidNameChars);
 
-                if (String.IsNullOrWhiteSpace(value))
-                    throw new ArgumentException("Worksheet names cannot be empty");
-
                 if (value.Length > 31)
                     throw new ArgumentException("Worksheet names cannot be more than 31 characters");
 
@@ -484,7 +484,7 @@
 
         public IXLWorksheet ExpandColumns()
         {
-            Enumerable.Range(1, 8).ForEach(i => ExpandRows(i));
+            Enumerable.Range(1, 8).ForEach(i => ExpandColumns(i));
             return this;
         }
 
@@ -989,6 +989,8 @@
 
             Internals.Dispose();
 
+            SelectedRanges?.Dispose();
+            DataValidations?.Dispose();
             this.Pictures.ForEach(p => p.Dispose());
 
             base.Dispose();
diff --git a/ClosedXML/XLHelper.cs b/ClosedXML/XLHelper.cs
index 0796264..76d2b7b 100644
--- a/ClosedXML/XLHelper.cs
+++ b/ClosedXML/XLHelper.cs
@@ -116,8 +116,10 @@
 
         public static bool IsValidColumn(string column)
         {
+            if (String.IsNullOrWhiteSpace(column))
+                return false;
             var length = column.Length;
-            if (String.IsNullOrWhiteSpace(column) || length > 3)
+            if (length > 3)
                 return false;
 
             var theColumn = column.ToUpper();