(gdb) run
Starting program: /tmp/536/test536 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
An error occurred: Cannot use empty keys in 'opts'.

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7053b8c in bson_destroy ()
   from /usr/lib/x86_64-linux-gnu/libbson-1.0.so.0
(gdb) bt all
No symbol "all" in current context.
(gdb) bt full
#0  0x00007ffff7053b8c in bson_destroy ()
   from /usr/lib/x86_64-linux-gnu/libbson-1.0.so.0
No symbol table info available.
#1  0x00007ffff7b97b28 in ?? ()
   from /usr/lib/x86_64-linux-gnu/libmongoc-1.0.so.0
No symbol table info available.
#2  0x0000555555554e98 in cause_crash (collection=0x555555774610) at test.c:38
        filter = 0x555555774530
        opts = 0x555555777c50
        cursor = 0x555555777d70
        error = {domain = 4, code = 16, 
          message = "Cannot use empty keys in 'opts'.\000\000\000\000\000\000\000\000\020\333\377\377\377\177\000\000@\261\003\367\001\000\000\000\377\377\377\377\377\377\377\377\000\000\000\000\000\000\000\000nFUUUU\000\000\020ִ\336\000\000\000\000\377\377\377\377\000\000\000\000\270t\005\367\377\177\000\000\060ٷ\367\377\177\000\000@\261\003\367\377\177", '\000' <repeats 11 times>, "\202 \204\327\312S\217`owUUU\000\000\377v\005\367\377\177\000\000\200\333\377\377\377\177\000\000\233\227\274\367\377\177\000\000 HwUUU\000\000\263w\005\367\377\177\000\000P\353\003\367\377\177\000\000\200\333\377\377\377\177\000\000p\334"...}
        doc = 0x0
        str = 0x555555555094 "test"
#3  0x0000555555554f8a in main (argc=1, argv=0x7fffffffe258) at test.c:69
        client = 0x555555776170
---Type <return> to continue, or q <return> to quit---
        collection = 0x555555774610
        error = {domain = 4294958752, code = 32767, 
          message = "\240\336\377\377\377\177\000\000\240>wUUU\000\000\261I\274\367\377\177\000\000\060\340\377\377\377\177\000\000\001\000\000\000\000\000\000\000,\000\000\000\000\000\000\000v\311\331\366\377\177\000\000\001\200\255\373\377\177\000\000\240>wUUU\000\000\240>wUUU\000\000\240>wUUU\000\000\240>wUUU\000\000\314>wUUU\000\000\314>wUUU\000\000\240>wUUU\000\000\314>wUUU", '\000' <repeats 46 times>, "\004", '\000' <repeats 15 times>, "n", '\000' <repeats 19 times>...}
        uristr = 0x555555555068 "mongodb://127.0.0.1/?appname=client-example"
        collection_name = 0x555555555094 "test"
        query = {flags = 4294958752, len = 32767, 
          padding = "\220\235\312\366\377\177\000\000\304\335\377\377\377\177\000\000\220\336\377\377\377\177\000\000\230k\375\367\377\177\000\000\f\000\000\000\000\000\000\000\320\336\377\377\000\000\000\000\220\235\312\366\377\177\000\000\364\335\377\377", '\000' <repeats 12 times>, "\230k\375\367\377\177\000\000 w\377\367\377\177\000\000\060\337\377\377\377\177\000\000(2\375\367\377\177\000\000\001", '\000' <repeats 14 times>}