BufferImageStim: maskParams argument documented but not supported

Attempting to set maskParams for BufferImageStim in PsychoPy v. 3.1.2 raises error:

TypeError: init() got an unexpected keyword argument ‘maskParams’

Although documented, bufferimagestim.py does not list maskParams in init(), nor include it in call to super(). Doing so gets the mask set as expected, without error. However, necessary to define default as

maskParams = None

not

maskParams = ‘None’

(as mask argument gets away with), otherwise …

ValueError: dictionary update sequence element #0 has length 1; 2 is required