cbimport should timeout and throw error when missing field-separator in non default field separator

Install Couchbase Server 4.6.0-3527
Create default bucket.
Import tab separator data with missing --field-separator flag. Command hang forever without throw out any error. I had to kill cbimport process to stop it.

[root@localhost ~]# /opt/couchbase/bin/cbimport csv -c 172.23.106.84 -u Administrator -p password -b default -d file:///tmp/import/csv_tab_1000_lines -g %index%
^Z
[1]+ Stopped /opt/couchbase/bin/cbimport csv -c 172.23.106.84 -u Administrator -p password -b default -d file:///tmp/import/csv_tab_1000_lines -g %index%

[root@localhost ~]# /opt/couchbase/bin/cbimport csv -c 172.23.106.84 -u Administrator -p password -b default -d file:///tmp/import/csv_tab_1000_lines --field-separator $'\t' -g %index%
CSV `file:///tmp/import/csv_tab_1000_lines` imported to `http://172.23.106.84:8091` successfully