nullはだめよ

javax.imageio.

throw new IllegalArgumentException("xxx == null!");

javax.swing.JList

throw new IllegalArgumentException("xxx must be non-null");

setの場合
if (columnModel == null) {
throw new IllegalArgumentException("Cannot set a null ColumnModel");
}

if (is == null) {
throw new IllegalArgumentException("InputStream cannot be null");
}

throw new IllegalArgumentException("String cannot be null");