Allow null values on nodes.

VAR.ExpressionEvaluator.Tests/ParserTests.cs

@@ -401,5 +401,45 @@ namespace VAR.ExpressionEvaluator.Tests
 
         #endregion BooleanOps
 
+        #region Null value
+
+
+        [TestMethod()]
+        public void NullValue_NullPlusAnything_EqualsNull()
+        {
+            Assert.AreEqual(null, Parser.EvaluateString("null + 1"));
+            Assert.AreEqual(null, Parser.EvaluateString("null + 100"));
+            Assert.AreEqual(null, Parser.EvaluateString("1 + null"));
+            Assert.AreEqual(null, Parser.EvaluateString("100 + null"));
+            Assert.AreEqual(null, Parser.EvaluateString("null + null"));
+        }
+
+        [TestMethod()]
+        public void NullValue_NullMinusAnything_EqualsNull()
+        {
+            Assert.AreEqual(null, Parser.EvaluateString("null - 1"));
+            Assert.AreEqual(null, Parser.EvaluateString("null - 100"));
+            Assert.AreEqual(null, Parser.EvaluateString("1 - null"));
+            Assert.AreEqual(null, Parser.EvaluateString("100 - null"));
+            Assert.AreEqual(null, Parser.EvaluateString("null - null"));
+        }
+
+        [TestMethod()]
+        public void NullValue_NullByAnything_EqualsNull()
+        {
+            Assert.AreEqual(null, Parser.EvaluateString("null * 1"));
+            Assert.AreEqual(null, Parser.EvaluateString("null * 100"));
+            Assert.AreEqual(null, Parser.EvaluateString("1 * null"));
+            Assert.AreEqual(null, Parser.EvaluateString("100 * null"));
+            Assert.AreEqual(null, Parser.EvaluateString("null * null"));
+
+            Assert.AreEqual(null, Parser.EvaluateString("null / 1"));
+            Assert.AreEqual(null, Parser.EvaluateString("null / 100"));
+            Assert.AreEqual(null, Parser.EvaluateString("1 / null"));
+            Assert.AreEqual(null, Parser.EvaluateString("100 / null"));
+            Assert.AreEqual(null, Parser.EvaluateString("null / null"));
+        }
+        
+        #endregion
     }
 }

VAR.ExpressionEvaluator/EvaluationContext.cs

@@ -39,6 +39,11 @@ namespace VAR.ExpressionEvaluator
 
         public void SetVariable(string name, object value)
         {
+            if (value is DBNull)
+            {
+                value = null;
+            }
+
             if (value is DateTime)
             {
                 value = ((DateTime)value).ToString("s");
@@ -60,7 +65,7 @@ namespace VAR.ExpressionEvaluator
         {
             if (_variables.ContainsKey(name) == false)
             {
-                return null;
+                throw new Exception(string.Format("Variable {0} not found", name));
             }
             return _variables[name];
         }

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionBooleanAndNode.cs

@@ -9,9 +9,10 @@
 
         private static object BooleanAndOp(object leftValue, object rightValue)
         {
-            bool bLeftValue = ExpressionBooleanNode.ConvertToBoolean(leftValue);
+            bool? bLeftValue = ExpressionBooleanNode.ConvertToBoolean(leftValue);
-            bool brightValue = ExpressionBooleanNode.ConvertToBoolean(rightValue);
+            bool? brightValue = ExpressionBooleanNode.ConvertToBoolean(rightValue);
-            return bLeftValue && brightValue;
+            if (bLeftValue == null || bLeftValue == null) { return null; }
+            return bLeftValue.Value && brightValue.Value;
         }
     }
 }

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionBooleanNode.cs

@@ -14,8 +14,13 @@
             return _value;
         }
 
-        public static bool ConvertToBoolean(object value)
+        public static bool? ConvertToBoolean(object value)
         {
+            if (value == null)
+            {
+                return null;
+            }
+
             if (value is bool)
             {
                 return (bool)value;

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionBooleanNotNode.cs

@@ -10,6 +10,7 @@
         private static object BooleanNotOp(object value)
         {
             value = ExpressionBooleanNode.ConvertToBoolean(value);
+            if (value == null) { return null; }
             return !(bool)value;
         }
     }

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionBooleanOrNode.cs

@@ -9,9 +9,10 @@
 
         private static object BooleanOrOp(object leftValue, object rightValue)
         {
-            bool bLeftValue = ExpressionBooleanNode.ConvertToBoolean(leftValue);
+            bool? bLeftValue = ExpressionBooleanNode.ConvertToBoolean(leftValue);
-            bool brightValue = ExpressionBooleanNode.ConvertToBoolean(rightValue);
+            bool? brightValue = ExpressionBooleanNode.ConvertToBoolean(rightValue);
-            return bLeftValue || brightValue;
+            if (bLeftValue == null || bLeftValue == null) { return null; }
+            return bLeftValue.Value || brightValue.Value;
         }
     }
 }

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionDivisionNode.cs

@@ -11,6 +11,11 @@ namespace VAR.ExpressionEvaluator
 
         private static object DivisionOp(object leftValue, object rightValue)
         {
+            if (leftValue == null || rightValue == null)
+            {
+                return null;
+            }
+
             if (leftValue is string)
             {
                 if (decimal.TryParse((string)leftValue, out decimal dec) == false)

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionEqualsNode.cs

@@ -11,6 +11,15 @@ namespace VAR.ExpressionEvaluator
 
         private static object EqualsOp(object leftValue, object rightValue)
         {
+            if (leftValue == null && rightValue == null)
+            {
+                return true;
+            }
+            if (leftValue == null || rightValue == null)
+            {
+                return false;
+            }
+
             if (leftValue is string && rightValue is string)
             {
                 return string.Compare((string)leftValue, (string)rightValue) == 0;

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionGreaterOrEqualThanNode.cs

@@ -11,6 +11,11 @@ namespace VAR.ExpressionEvaluator
 
         private static object GreaterOrEqualThanOp(object leftValue, object rightValue)
         {
+            if (leftValue == null || rightValue == null)
+            {
+                return false;
+            }
+
             if (leftValue is string && rightValue is string)
             {
                 return string.Compare((string)leftValue, (string)rightValue) >= 0;

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionGreaterThanNode.cs

@@ -11,6 +11,11 @@ namespace VAR.ExpressionEvaluator
 
         private static object GreaterThanOp(object leftValue, object rightValue)
         {
+            if (leftValue == null || rightValue == null)
+            {
+                return false;
+            }
+
             if (leftValue is string && rightValue is string)
             {
                 return string.Compare((string)leftValue, (string)rightValue) > 0;

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionLessOrEqualThanNode.cs

@@ -11,6 +11,11 @@ namespace VAR.ExpressionEvaluator
 
         private static object LessOrEqualThanOp(object leftValue, object rightValue)
         {
+            if (leftValue == null || rightValue == null)
+            {
+                return false;
+            }
+
             if (leftValue is string && rightValue is string)
             {
                 return string.Compare((string)leftValue, (string)rightValue) <= 0;

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionLessThanNode.cs

@@ -11,6 +11,11 @@ namespace VAR.ExpressionEvaluator
 
         private static object LessThanOp(object leftValue, object rightValue)
         {
+            if (leftValue == null || rightValue == null)
+            {
+                return false;
+            }
+
             if (leftValue is string && rightValue is string)
             {
                 return string.Compare((string)leftValue, (string)rightValue) < 0;

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionMinusNode.cs

@@ -11,6 +11,11 @@ namespace VAR.ExpressionEvaluator
 
         private static object MinusOp(object leftValue, object rightValue)
         {
+            if (leftValue == null || rightValue == null)
+            {
+                return null;
+            }
+
             if (leftValue is string)
             {
                 if (decimal.TryParse((string)leftValue, out decimal dec) == false)

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionMultiplyNode.cs

@@ -11,6 +11,11 @@ namespace VAR.ExpressionEvaluator
 
         private static object MultiplyOp(object leftValue, object rightValue)
         {
+            if (leftValue == null || rightValue == null)
+            {
+                return null;
+            }
+
             if (leftValue is string)
             {
                 if (decimal.TryParse((string)leftValue, out decimal dec) == false)

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionNotEqualsNode.cs

@@ -11,6 +11,15 @@ namespace VAR.ExpressionEvaluator
 
         private static object NotEqualsOp(object leftValue, object rightValue)
         {
+            if (leftValue == null && rightValue == null)
+            {
+                return false;
+            }
+            if (leftValue == null || rightValue == null)
+            {
+                return true;
+            }
+
             if (leftValue is string && rightValue is string)
             {
                 return string.Compare((string)leftValue, (string)rightValue) != 0;

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionNullNode.cs

@@ -0,0 +1,10 @@
+namespace VAR.ExpressionEvaluator
+{
+    public class ExpressionNullNode : IExpressionNode
+    {
+        public object Eval(IEvaluationContext evaluationContext)
+        {
+            return null;
+        }
+    }
+}

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionNumberNegateNode.cs

@@ -11,6 +11,11 @@ namespace VAR.ExpressionEvaluator
 
         private static object NumberNegateOp(object value)
         {
+            if (value == null)
+            {
+                return null;
+            }
+
             if (value is string)
             {
                 if (decimal.TryParse((string)value, out decimal dec) == false)

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionPlusNode.cs

@@ -11,6 +11,11 @@ namespace VAR.ExpressionEvaluator
 
         private static object PlusOp(object leftValue, object rightValue)
         {
+            if (leftValue == null || rightValue == null)
+            {
+                return null;
+            }
+
             if (leftValue is string || rightValue is string)
             {
                 return string.Concat(Convert.ToString(leftValue), Convert.ToString(rightValue));

VAR.ExpressionEvaluator/ExpressionNodes/ExpressionVariableNode.cs

@@ -14,10 +14,6 @@ namespace VAR.ExpressionEvaluator
         public object Eval(IEvaluationContext evaluationContext)
         {
             object value = evaluationContext.GetVariable(_name);
-            if (value == null)
-            {
-                throw new Exception(string.Format("Variable {0} not found", _name));
-            }
             return value;
         }
     }

VAR.ExpressionEvaluator/Parser.cs

@@ -197,6 +197,11 @@ namespace VAR.ExpressionEvaluator
                     _tokenizer.NextToken();
                     return new ExpressionBooleanNode(false);
                 }
+                if (identifierToLower == "null")
+                {
+                    _tokenizer.NextToken();
+                    return new ExpressionNullNode();
+                }
 
                 string identifier = _tokenizer.Text;
                 _tokenizer.NextToken();

VAR.ExpressionEvaluator/VAR.ExpressionEvaluator.csproj

@@ -55,6 +55,7 @@
     <Compile Include="ExpressionNodes\ExpressionLessThanNode.cs" />
     <Compile Include="ExpressionNodes\ExpressionMultiplyNode.cs" />
     <Compile Include="ExpressionNodes\ExpressionNotEqualsNode.cs" />
+    <Compile Include="ExpressionNodes\ExpressionNullNode.cs" />
     <Compile Include="ExpressionNodes\ExpressionUnaryNode.cs" />
     <Compile Include="ExpressionNodes\ExpressionBinaryNode.cs" />
     <Compile Include="ExpressionNodes\ExpressionMinusNode.cs" />