docs: def _preprocess(argument, casesensitive):
          """Receives the argument (from the constructor), and normalizes it
          into a list of Pattern objects."""
          pattern_set = PatternSet()
          if argument is not None:
              if isinstance(argument, STRING_TYPES):
                  argument = [argument, ]
  
              for glob in argument:
                  if isinstance(glob, str):
                      patterns = Pattern.create(glob, casesensitive)
                      pattern_set.extend(patterns)
  
                  elif isinstance(glob, Pattern):
                      pattern_set.append(glob)
  
          return pattern_set