develop-when running coverage html - the 'null code coverage' is shown as title

When running `ut_html_coverage_reporter` from SQL Developer - I get: 
`<title>Code coverage</title>`
When running from cli I get:
`<title>null code coverage</title>`
It seems that you're calling constructor with  'null' as a string:
`ut_coverage_html_reporter('null')`
Rather than calling it with an actual null:
`ut_coverage_html_reporter(null)`