code: @Nullable
    public <T> T toObject(@Nonnull Class<T> valueType) {
      Map<String, Object> data = getData();
      return data == null ? null : CustomClassMapper.convertToCustomClass(getData(), valueType);
    }
docs: Returns the contents of the document converted to a POJO or null if the document doesn't exist.
  
  @param valueType The Java class to create
  @return The contents of the document in an object of type T or null if the document doesn't
  exist.