The expression return $this->getStrictP...ocument::TAG_OPERATION) returns the type WsdlToPhp\DomHandler\ElementHandler which includes types incompatible with the type-hinted return WsdlToPhp\WsdlHandler\Tag\TagOperation|null.
This check compares calls to functions or methods with their respective definitions.
If the call has more arguments than are defined, it raises an issue.
If a function is defined several times with a different number of parameters, the
check may pick up the wrong definition and report false positives. One codebase
where this has been known to happen is Wordpress. Please note the @ignore annotation hint above.