Question about eglCreatePbufferSurface with empty attrib_list

Hi,
In spec, eglCreatePbufferSurface is allowed to be called with attrib_list is NULL or empty, which means EGL_WIDTH/EGL_HEIGHT for the surface is 0.
And in mesa code, specific to android path, I cannot find the width/height could be updated to a normal value.
Also the eglMakeCurrent call after the eglCreatePbufferSurface, will use the 0 width/height to allocate buffer, which seems un-reasonable.
Could you share me why 0 is allowed for width/height, and how app will use the PbufferSurface later?
Thanks.

Best Regards
Shuicheng