code: public static ImmutableMap<String, String> loadStringMapAllowingEmptyValues(CharSource source)
        throws IOException {
      return loadStringMap(source, true);
    }
docs: Like {@link #loadStringMap(CharSource)}, but differs in that lines can contain only
  a key and no value and will be treated as having a value of empty string in the resulting
  map. This is useful for specifying absent values for a specific key.
  
  @see FileUtils#loadStringMap(CharSource)