Error badmatch start_object decoder null 16 17 trim mochijson2 json_de

Error: {badmatch,{start_object,{decoder,null,16,1,17,trim}}}

[{mochijson2,json_decode,2},
 {couch_query_servers,read_json,1},
 {couch_query_servers,prompt,2},
 {couch_query_servers,'-map_docs/2-fun-1-',2},
 {lists,map,2},
 {lists,map,2},
 {couch_query_servers,map_docs,2},
 {couch_view,view_compute,2}]