The expression ImplicitReturnNode returns the type null which is incompatible with the return type mandated by Gacela\Framework\Setup\A...upGacela::buildConfig() of Gacela\Framework\Config\...igBuilder\ConfigBuilder.
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.}}