The expression return $trim ? trim($content) : $content could return the type array|null which is incompatible with the type-hinted return string. Consider adding an additional type-check to rule them out.
It seems like $content can also be of type array and null; however, parameter $string of trim() does only seem to accept string, maybe add an additional type check?
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Ignorable by Annotation
)
If this is a false-positive, you can also ignore this issue in your code via the ignore-type annotation
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.