IWF-124: Ignore empty output for collector

[lwolczynski]

Description

Checklist

• Code compiles correctly
• Tests for the changes have been added
• All tests passing
• This PR change is backwards-compatible
• This PR CONTAINS a (planned) breaking change (it is not backwards compatible)

Related Issue

Closes #issue_number

[longquanzheng]

lgtm,
do we know we have existing test with output(we probably do)
if no, can we change one of the test to return a non-nil output so that we can test the case?

[lwolczynski]

lgtm, do we know we have existing test with output(we probably do) if no, can we change one of the test to return a non-nil output so that we can test the case?

basic_test.go:
assertions.Equal(1, len(resp2.GetResults()))

conditional_close_test.go:
assertions.Equal(1, len(resp2.GetResults()))
assertions.Equal(expectedOutput, resp2.GetResults()[0])

skip_start_test.go:
assertions.Equal(1, len(resp2.GetResults()))