use in in if result not as exepected

[jiangbo0216]

	tpl, err := pongo2.FromString(`{% for el in ssrCatalogList %} {% if "number" in (el.OlType) %} {{forloop.Counter}} {% endif %} {%endfor%}`)
	if err != nil {
		panic(err)
	}
	if err != nil {
		panic(err)
	}

	// Now you can render the template with the given
	// pongo2.Context how often you want to.
	out, err := tpl.Execute(pongo2.Context{"ssrCatalogList": []interface{}{
		map[string]string{"IsTitle": "number1234567890", "Text": "fdfd", "OlType": "dsdsnumberdsds"},
		map[string]string{"IsTitle": "number1234567890", "Text": "ffff"},
	}})
	if err != nil {
		panic(err)
	}
	fmt.Println(out) // Output: Hello Florian!

	tpl, err := pongo2.FromString(`{% for el in ssrCatalogList %} {% if "number" in (el.OlType or "") %} {{forloop.Counter}} {% endif %} {%endfor%}`)
	if err != nil {
		panic(err)
	}
	if err != nil {
		panic(err)
	}

	// Now you can render the template with the given
	// pongo2.Context how often you want to.
	out, err := tpl.Execute(pongo2.Context{"ssrCatalogList": []interface{}{
		map[string]string{"IsTitle": "number1234567890", "Text": "fdfd", "OlType": "dsdsnumberdsds"},
		map[string]string{"IsTitle": "number1234567890", "Text": "ffff"},
	}})
	if err != nil {
		panic(err)
	}
	fmt.Println(out) // Output: Hello Florian!

the only diff is "number" in (el.OlType or "") and "number" in el.OlType, the result is different