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From Mike Kienenberger <>
Subject JSF 2.1.3: default Myfaces error handling cannot deal with a null component.getValueExpression(name)
Date Mon, 28 Nov 2011 17:32:50 GMT
I'm debugging a JSF application which is being upgraded from JSF
1.2+Richfaces 3.3 to JSF 2.1+Richfaces4.1.
When it hits an error, I get sent to the default MyFaces error handling.

I'm noticing that the default error handling is hitting an NPE in
org.apache.myfaces.renderkit.ErrorPageWriter:line 1305 on the
for "rendered" on the __rf_skinning_resource UIOutput automatically
being handled in the <head> tag.

                        valueExpression = c.getValueExpression(pd[i].getName());
                        if (valueExpressionValues && valueExpression != null)
                            _writeAttribute(writer, pd[i].getName(),

This expression string is hardcoded to return null (subclass of

>From what I can tell, it's legal for a value expression to return null.

In any case, since this is an error handling routine, it should
probably be more flexible in handling unexpected values.

What do we want to do in this case?

We could skip outputting the attribute.

We could output the attribute with empty string as the value
expression.   In this particular case, we could check for isReadOnly()
and if true, output getValue().   Not sure if we'd want to do that in
the case of !isReadOnly().  In fact, I'm not entirely certain we want
to be evaluating getValue().

We could output the class of the value expression.

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