FIX Invalid return for NoopTracer::startSpan

[fredipevcin]

Short description of what this PR does:

NoopTracer::startSpan was returning null instead of Span

Checklist

• [x] I have made a material change to the repo (functionality, testing, spelling, grammar)
• [ ] I have read the [Contribution Guide] and my PR follows them.
• [x] I updated my branch with the master branch.
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation about the functionality in the appropriate .md file
• [ ] I have added in line documentation to the code I modified

[jcchavezs]

Thanks @fredipevcin