Segfault on bogus rocksdb_tmpdir and custom column family

CREATE DATABASE test;
USE test;
set session rocksdb_tmpdir='a';
CREATE TABLE t1(c1 YEAR,c2 BINARY,c3 INT,c4 BINARY KEY,c5 YEAR UNIQUE KEY,c6 DECIMAL(0,0)DEFAULT 3.141592) ENGINE=ROCKSDB;
CREATE INDEX i1_3 ON t1(c1,c2,c3) COMMENT '0';
DROP TABLE t1;

Thread 7 "myrocks-index" received signal SIGABRT, Aborted.
[Switching to Thread 0x7fffe97fa700 (LWP 10381)]
__GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
51      ../sysdeps/unix/sysv/linux/raise.c: No such file or directory.
(gdb) bt
#0  __GI_raise (sig=sig@entry=6) at ../sysdeps/unix/sysv/linux/raise.c:51
#1  0x00007ffff5915801 in __GI_abort () at abort.c:79
#2  0x0000555556bca5b9 in myrocks::Rdb_drop_index_thread::run (this=0x555557f3bc80 <myrocks::rdb_drop_idx_thread>) at /home/glorch/dev/ps/facebook-mysql/storage/rocksdb/ha_rocksdb.cc:10835
#3  0x0000555556c97202 in myrocks::Rdb_thread::thread_func (thread_ptr=0x555557f3bc80 <myrocks::rdb_drop_idx_thread>) at /home/glorch/dev/ps/facebook-mysql/storage/rocksdb/rdb_threads.cc:32
#4  0x0000555556ba051c in pfs_spawn_thread (arg=0x555558378b70) at /home/glorch/dev/ps/facebook-mysql/storage/perfschema/pfs.cc:1860
#5  0x00007ffff660c6db in start_thread (arg=0x7fffe97fa700) at pthread_create.c:463
#6  0x00007ffff59f688f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95