code: def is_kana(text):
      ''' Check if a text if written in kana only (hiragana & katakana)
      if text is empty then return True
      '''
      if text is None:
          raise ValueError("text cannot be None")
      for c in text:
          if c not in HIRAGANA and c not in KATAKANA:
              return False
      return Truf is_kana(text):
      ''' Check if a text if written in kana only (hiragana & katakana)
      if text is empty then return True
      '''
      if text is None:
          raise ValueError("text cannot be None")
      for c in text:
          if c not in HIRAGANA and c not in KATAKANA:
              return False
      return True
docs: Check if a text if written in kana only (hiragana & katakana)
      if text is empty then return True