debug jsonDoc_to_mentions

[maxaalexeeva]

The endpoint described here https://github.com/ml4ai/automates/wiki/Text-Reading#mention-extraction- results in some mentions with null paths, which can't be handled by the align endpoint (JNull error). If input is supposed to be the processors document, the wiki will need to be updated with an extra step, but it is probably more convenient for users to not have extra steps, so just make sure the endpoint takes a science parse doc and produces mentions of the right format. (also, check if the pdf_to_mentions produces mentions that can be handled by align)