500 Internal Server Error

Technical details:
Error: access to uninitialised variable - (array element 1)
***  in function "JPR_get_array_metadata_structured_data"
***  line: {L1}[-1] = ["citation_author", ({L8})[{L9}]] : 0
***  call: JPR_get_array_metadata_structured_data ()
***  call: JPR_output_array_meta_tags ()