I tried to migrate some portlets from 2.3.4 to 2.3.7 (actually to 2.3.15 but have found that the problem starts in 2.3.7)
What happens is there is now a warning in the logs whenever I execute an action.
09:33:35,327 WARN [OgnlValueStack:60] Error setting expression 'struts.portlet.action' with value '[Ljava.lang.String;@78f28bba'
ognl.OgnlException: source is null for getProperty(null, "portlet")
It seems that in older versions of struts portlet plugin this parameter use to be taken out, since I believe it is used by struts2 to know what action to execute, but should maybe not be stored in the OGNL stack. My guess is that this has to do with no field called 'portlet' with property 'action' in my action class existing to place the expression.
In version 18.104.22.168 and previous this was not an issue. Maybe the portlet interceptor was taking this parameters out before it was placed into OGNL, and now it is being left?