The expression return $this returns the type leocata\M1\InternalFunctionality\MonologHandler which is incompatible with the return type mandated by Monolog\Handler\AbstractProcessingHandler::write() of void.
In the issue above, the returned value is violating the contract defined by the
mentioned interface.
Let's take a look at an example:
interfaceHasName{/** @return string */publicfunctiongetName();}className{public$name;}classUserimplementsHasName{/** @return string|Name */publicfunctiongetName(){returnnewName('foo');// This is a violation of the ``HasName`` interface// which only allows a string value to be returned.}}
This check looks for assignments to scalar types that may be of the wrong type.
To ensure the code behaves as expected, it may be a good idea to add an explicit type cast.