if(core == null) return;
if(val.equals(get()) || val.equals(""))
cssOverride = null;
else {
File tmp = new File(val.trim());
if(!core.allowUploadFrom(tmp))
throw new InvalidConfigValueException(l10n("cssOverrideNotInUploads", "filename", tmp.toString()));
else if(!tmp.canRead() || !tmp.isFile())
throw new InvalidConfigValueException(l10n("cssOverrideCantRead", "filename", tmp.toString()));
File parent = tmp.getParentFile();
// Basic sanity check.