def find_referenced_subfiles(self, directory):
        """
        Return list of files below specified `directory` in job inputs. Could
        use more sophisticated logic (match quotes to handle spaces, handle
        subdirectories, etc...).

        **Parameters**

        directory : str
            Full path to directory to search.

        """
        if directory is None:
            return []

        pattern = r'''[\'\"]?(%s%s[^\s\'\"]+)[\'\"]?''' % (escape(directory), escape(sep))
        return self.find_pattern_references(pattern)