code: public boolean containsKey(String key, Charset charset)
      {
          return meta.containsKey(BinaryValue.unsafeCreate(key.getBytes(charset)));
      }
docs: Determine if a specific usermeta entry is present.
  <p>
  This method uses the supplied {@code Charset} to convert the supplied key.
  </p>
  
  @param key the metadata key
  @return {@code true} if the entry is present, {@code false} otherwise.