Seen two separate issues.
First, when there was a mismatch in arguments to parameters (see
ISIS-1497), this resulted in an NPE in this line of the catch block:
specifically, getPriorExecution() returned null.
Then, when I worked around that issue so that the action could be invoked but when executed threw an exception, resulted in an NPE in this line of the catch block:
Here, getCurrentExecution() returned null.