"if not" condition not working properly

[dgofman]

Open file: pongo2/template_tests/if.tpl and add two conditions after this line:
{% if "Text" in complex.post %}text field in complex.post{% endif %}

Hello string {% if not "Hello" in complex.post.Text %}is not{% else %}is{% endif %} in complex.post.Text
World string {% if not "World" in complex.post.Text %}is not{% else %}is{% endif %} in complex.post.Text

In pongo2_template_test.go the "complex.post.Text" = <h2>Hello!</h2><p>Welcome...

So, we are expecting the "World" does not exist in the string we should get two different results, However result are:

 Hello string is in complex.post.Text
 World string is in complex.post.Text

[dgofman]

Open the file parser_expression.go, the problem in "result = result.Negate()". It may work for Boolean types but definitely not for String.

func (expr *simpleExpression) Evaluate(ctx *ExecutionContext) (*Value, *Error) {
	t1, err := expr.term1.Evaluate(ctx)
	if err != nil {
		return nil, err
	}
	result := t1

	if expr.negate {
		result = result.Negate()
	}

Such as common function for backward compatibility I implemented the fix in that function:
"func (expr *relationalExpression) Evaluate(ctx *ExecutionContext) (*Value, *Error) {"

                   case "in":
			val, ok := expr.expr1.(*simpleExpression)
			if ok && val.negate {
				t1, err := val.term1.Evaluate(ctx)
				if err == nil {
					return AsValue(!v2.Contains(t1)), nil
				}
			}
			return AsValue(v2.Contains(v1)), nil

[dgofman]

I opened a pull request

#210