Find mismatching @return annotations

[quasilyte]

Code Example

    /**
     * Set the current local namespace.
     * @param array|null $namespace (default: null)
     * @return array|null
     */
    public function setNamespace(array $namespace = null)
    {
        $this->namespace = $namespace;
    }

Actual Behavior

No warnings.

Expected Behavior

Warning about not returning anything from a function that promised to return something (except null) in its phpdoc.

[i582]

Will be tracked further in #1123.