fix: addition of null and bubble container

Author: nekosaur

CodingSeb.ExpressionEvaluator.Tests/ExpressionEvaluatorTests.cs

@@ -1,4 +1,5 @@
-using Newtonsoft.Json;
+using Microsoft.CSharp.RuntimeBinder;
+using Newtonsoft.Json;
 using NUnit.Framework;
 using Shouldly;
 using System;
@@ -1837,6 +1838,15 @@ public void Evaluate_DoubleDoubleQuotesInEscapedStringThrowException()
 
             evaluator.Evaluate("@\"Hello \"\" Joe\"").ShouldBe(@"Hello "" Joe");
         }
+        
+        [Test]
+        [Category("Bug")]
+        public void Evaluate_NullAdditionShouldThrowExceptionNotReturnString()
+        {
+            var evaluator = new ExpressionEvaluator();
+
+            Should.Throw<RuntimeBinderException>(() => evaluator.Evaluate("(null + null) + null"));
+        }
 
         //[Test]
         //[Category("Bug")]

CodingSeb.ExpressionEvaluator/ExpressionEvaluator.cs

@@ -3296,11 +3296,11 @@ void EvaluateFirstPreviousUnaryOp(int j)
                                 {
                                     list[i] = operatorEvalutationsDict[eOp](left, right);
 
-                                    if (left is BubbleExceptionContainer && right is string)
+                                    if (left is BubbleExceptionContainer && right is string or null)
                                     {
                                         list[i] = left; //Bubble up the causing error
                                     }
-                                    else if (right is BubbleExceptionContainer && left is string)
+                                    else if (right is BubbleExceptionContainer && left is string or null)
                                     {
                                         list[i] = right; //Bubble up the causing error
                                     }