I18nMessage - null parameter values causes NPE

Putting a null in a parameter value causes an NPE when creating the SAX events

java.lang.NullPointerException
at org.apache.cocoon.forms.util.I18nMessage.toSAX(I18nMessage.java:128)
at org.apache.cocoon.forms.validation.ValidationError.generateSaxFragment(ValidationError.java:85)
at org.apache.cocoon.forms.formmodel.Field.generateItemSaxFragment(Field.java:453)
at org.apache.cocoon.forms.formmodel.AbstractWidget.generateSaxFragment(AbstractWidget.java:498)
at org.apache.cocoon.forms.generation.JXMacrosHelper.generateWidget(JXMacrosHelper.java:292)

Note: this NPE then causes the Ajax transformer to go wonky for all users in all sessions. I'm still digging into that one.

I am attaching a patch (license granted to ASF) that allows null parameter values (using String.valueOf(parameters[i]) so that nulls are turned into "null".