I recently got the error message "Argument Error: One or more parameters are null." when trying to load a JSF page. It confused me at first because I'd not seen this particular message before. I quickly realized what was causing the problem but it wasn't immediatly obvious why it was causing it.

SEVERE: Servlet.service() for servlet Faces Servlet 
threw exception
java.lang.NullPointerException: Argument Error: One or more parameters are null.
  at com.sun.faces.renderkit.html_basic.HtmlResponseWriter.writeText(HtmlResponseWriter.java:357)
  at com.sun.faces.renderkit.html_basic.MenuRenderer.renderOption(MenuRenderer.java:581)
  at com.sun.faces.renderkit.html_basic.MenuRenderer.renderOptions(MenuRenderer.java:525)
  at com.sun.faces.renderkit.html_basic.MenuRenderer.renderSelect(MenuRenderer.java:481)
  at com.sun.faces.renderkit.html_basic.MenuRenderer.encodeEnd(MenuRenderer.java:430)

The offending code was similar to the following snippet.

The problem is that there is no itemLabel attribute. Rather than issuing a warning that itemLabel is not present error message (as it normally does with what should be a schema violation) it falls over with a NullPointer.

The reason I'd not seen this message before is because I haven't directly specified the selection items in the page before.