If the Head.PARSE_CONTENT is not available in the context the relevant Dojo tag throws a NPE.
Undoubtedly users will frequently forget to set parseContent on the page's head tag, or on the respective widget tag so this patch provides default handling for the case where parseContent is null.
The objective of this patch is to reduce the potential for support queries regarding the NPE within struts 2.
The patch is the equivalent to
WW-2398 only the affected code is repeated in Tree, TabbedPanel, Autocompleter, Submit, TreeNode, DateTimePicker and TextArea
See also dev discussion: http://firstname.lastname@example.org/msg30811.html