code: public void addPreloadFont (@Nonnull final PreloadFont aPreloadFont)
    {
      ValueEnforcer.notNull (aPreloadFont, "PreloadFont");
      final String sKey = aPreloadFont.getID ();
  
      m_aRWLock.writeLocked ( () -> {
        if (m_aMap.containsKey (sKey))
          throw new IllegalArgumentException ("The PreloadFont  " + aPreloadFont + " is already contained!");
        m_aMap.put (sKey, aPreloadFont);
      });
    }
docs: Add a pre-created {@link PreloadFont}.
  
  @param aPreloadFont
  The font to be added. May not be <code>null</code>.