It seems like $header defined by $this->replaceHeader($he...が発生しました') on line 42 can also be of type false; however, Risoluto\RisolutoViewTrait::replaceHeader() does only seem to accept array, did you maybe forget to handle an error condition?
This check looks for type mismatches where the missing type is false. This
is usually indicative of an error condtion.
This function either returns a new DateTime object or false, if there was an error.
This is a typical pattern in PHP programming to show that an error has occurred without
raising an exception. The calling code should check for this returned false
before passing on the value to another function or method that may not
be able to handle a false.