UBSAN reports:
evbuffer/remove_buffer_with_empty3: ../buffer.c:1443:3: runtime error: null pointer passed as argument 2, which is declared to never be null
#0 0x7ffff6cd0410 in evbuffer_pullup ../buffer.c:1443
#1 0x5555556d68b9 in test_evbuffer_remove_buffer_with_empty3 ../test/regress_buffer.c:408
#2 0x5555557b95ee in testcase_run_bare_ ../test/tinytest.c:173
#3 0x5555557ba048 in testcase_run_one ../test/tinytest.c:333
#4 0x5555557bc0f8 in tinytest_main ../test/tinytest.c:527
#5 0x555555787702 in main ../test/regress_main.c:528
#6 0x7ffff606c001 in __libc_start_main (/usr/lib/libc.so.6+0x27001)
#7 0x55555569436d in _start (/src/le/libevent/.cmake-debug/bin/regress+0x14036d)
a0c642ac04