Seems harmless in an Opis library, but it does cause FML to warn:
[20:21:58] [Client thread/WARN] [FML]: =============================================================
[20:21:58] [Client thread/WARN] [FML]: MOD HAS DIRECT REFERENCE System.exit() THIS IS NOT ALLOWED REROUTING TO FML!
[20:21:58] [Client thread/WARN] [FML]: Offendor: mcp/mobius/opis/gui/font/TrueTypeFont.loadImage(Ljava/awt/image/BufferedImage;)I
[20:21:58] [Client thread/WARN] [FML]: Use FMLCommonHandler.exitJava instead
[20:21:58] [Client thread/WARN] [FML]: =============================================================
Seems harmless in an Opis library, but it does cause FML to warn: