public ExprNodeMismatchWarning(int line, ExprNode expected, ExprNode actual, string message = "Expressions differ")
 {
     if (expected.Equals(actual))
     {
         throw new ArgumentException("Expected different objects");
     }
     this.Expected = expected;
     this.Actual   = actual;
     this.Message  = message;
     this.Line     = line;
 }