Add nil pointer checker when reading port value to avoid panic.

[csfmomo]

fix: add nil pointer checker when reading port value to avoid panic.

Reason for Change:
When generating network policy, customer could forget to fill in port value. No port value will result in panic due to nil pointer. Add check to avoid it.

fix: Bug Fixes 🐞

• [X ] adds unit tests

[codecov]

Codecov Report

Merging #606 into master will decrease coverage by 0.46%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #606      +/-   ##
==========================================
- Coverage   39.88%   39.41%   -0.47%     
==========================================
  Files          42       47       +5     
  Lines        4586     5178     +592     
==========================================
+ Hits         1829     2041     +212     
- Misses       2502     2870     +368     
- Partials      255      267      +12     

[matmerr]

thanks for the test yaml, lgtm