Cannot rewrite empty field nodes

[morgante]

Currently, if a field is null we can't rewrite/insert into it (because we don't have an associated range for a field that wasn't found).

Workaround

Rewrite the entire parent node that contained the null field.

Example

engine marzano(0.1)
language python

pattern test_func($name, $parameters, $return_type, $body) {
    function_definition($name, $parameters, $return_type, $body) as $function where {
        $name <: r"test_.*",
    }
}

pattern test_class($name, $superclasses, $body) {
    class_definition($name, $superclasses, $body) as $cls where {
        $superclasses <: contains `TestCase`,
    }
}

test_func($return_type) as $function where {
    $function <: within test_class(),
    $return_type => `None`
}