topic parse error should be checked

#### Expected behavior
`ParseTopicName()` parses topic and its return error should be check,
but currently the `err` is just omitted by assigning to _.
this causes runtime panic.

Start by locating ParseTopicName() and the call that assigns its returned error to _. Trace how the ignored error leads to the runtime panic, then verify that the relevant existing tests prevent the panic once the error is checked.

Written by the indexing model from the issue text.