Fix mixed return type for filter callbacks

[Hug0-Drelon]

Issue:

I get the following error for a filter callback with a mixed return type:

Filter callback return statement is missing.

This occurs with a callback like this:

/**
 * Does things.
 *
 * @param mixed  $param  Some value.
 * @return mixed
 */
function do_things( $param ) {
    // Do things
    return $param
}

IMHO this is due to this line where we get MixedType which seems to be a super type of VoidType (maybe because it include NullType.

Proposal:

• Add a special case for MixedType.
• Add a test for a callback with mixed return type.

[szepeviktor]

@herndlm @johnbillion Please help @Hug0-Drelon with his issue.

[szepeviktor]

I think "we" are working on this in #130

[Hug0-Drelon]

Oops, I should have look into previous PRs... Sorry.
Also, I have a hard time to run PHPUnit, for unknown reason it doesn't work locally...

[szepeviktor]

I have a hard time to run PHPUnit

Set memory_limit in your php.ini: #129

[Hug0-Drelon]

Useless since #130 is merged and fixed the issue.