code: public final void addCustomResponseHeader (@Nonnull @Nonempty final String sName,
                                               @Nonnull @Nonempty final String sValue)
    {
      ValueEnforcer.notEmpty (sName, "Name");
      ValueEnforcer.notEmpty (sValue, "Value");
  
      m_aResponseHeaderMap.addHeader (sName, sValue);
    }
docs: Adds a response header to the response according to the passed name and
  value. If an existing header with the same is present, the value is added
  to the list so that the header is emitted more than once.<br>
  <b>ATTENTION:</b> You should only use the APIs that {@link UnifiedResponse}
  directly offers. Use this method only in emergency and make sure you
  validate the header field and allowed value!
  
  @param sName
  Name of the header. May neither be <code>null</code> nor empty.
  @param sValue
  Value of the header. May neither be <code>null</code> nor empty.