code: public static ImmutableMap<Symbol, Symbol> loadSymbolMap(CharSource source) throws IOException {
      final ImmutableMap.Builder<Symbol, Symbol> ret = ImmutableMap.builder();
  
      for (ImmutableMap.Entry<String, String> row : loadStringMap(source).entrySet()) {
        ret.put(Symbol.from(row.getKey()), Symbol.from(row.getValue()));
      }
  
      return ret.build();
    }
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.