It seems like $this->options->eol can also be of type null; however, parameter $glue of implode() 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 looks for parameters that have been defined for a function or method, but which are not used in the method body.