code: public MustacheEngineBuilder registerHelpers(Map<String, Helper> helpers,
              boolean overwrite) {
          checkArgumentNotNull(helpers);
          checkNotBuilt();
          for (Entry<String, Helper> entry : helpers.entrySet()) {
              registerHelper(entry.getKey(), entry.getValue(), overwrite);
          }
          return this;
      }
docs: Each helper must be registered with a unique name. If there is a helper
  registered with the same name and the param <code>overwrite</code> is
  <code>true</code> the previous instance is replaced, otherwise an
  {@link IllegalArgumentException} is thrown.
  
  @param helpers
  @param overwrite
  @return