code: @Nonnull
    public PreloadFont getOrAddEmbeddingPreloadFont (@Nonnull final IFontResource aFontRes)
    {
      ValueEnforcer.notNull (aFontRes, "FontRes");
      PreloadFont aPreloadFont = getPreloadFontOfID (aFontRes);
      if (aPreloadFont == null)
      {
        aPreloadFont = PreloadFont.createEmbedding (aFontRes);
        addPreloadFont (aPreloadFont);
      }
      return aPreloadFont;
    }
docs: Create and add a new embedding {@link PreloadFont} if it is not yet
  contained.
  
  @param aFontRes
  The font resource to be added for embedding. May not be
  <code>null</code>.
  @return The created {@link PreloadFont}. Never <code>null</code>.