code: @Nonnull
    public T set(@Nonnull DocumentReference documentReference, @Nonnull Map<String, Object> fields) {
      return set(documentReference, fields, SetOptions.OVERWRITE);
    }
docs: Overwrites the document referred to by this DocumentReference. If the document doesn't exist
  yet, it will be created. If a document already exists, it will be overwritten.
  
  @param documentReference The DocumentReference to overwrite.
  @param fields A map of the field paths and values for the document.
  @return The instance for chaining.