code: public static void writeNullableString(@Nullable String str, DataOutputView out) throws IOException {
  		if (str != null) {
  			out.writeBoolean(true);
  			writeString(str, out);
  		} else {
  			out.writeBoolean(false);
  		}
  	}
docs: Writes a String to the given output. The string may be null.
  The written string can be read with {@link #readNullableString(DataInputView)}-
  
  @param str The string to write, or null.
  @param out The output to write to.
  
  @throws IOException Thrown, if the writing or the serialization fails.