code: public static ImmutableMap<String, String> loadStringMap(CharSource source) throws IOException {
      return loadStringMap(source, false);
    }
docs: Loads a file in the format {@code key value1} (tab-separated) into a {@link
  com.google.common.collect.ImmutableMap} of {@link String}s. Each key should only appear on one
  line, and there should be no duplicate values. Each key and value has whitespace trimmed off.
  Skips empty lines and allows comment-lines with {@code #} in the first position.