fix NPE when parsing null options used by conditions (fixes #133)

[cs-cat]

fix NPE when parsing null options used by conditions (fixes #133)

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[cs-cat]

I have read the CLA Document and I hereby sign the CLA

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.90%. Comparing base (9eb966e) to head (27312c1).

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Additional details and impacted files

@@             Coverage Diff              @@
##             master     #134      +/-   ##
============================================
- Coverage     71.91%   71.90%   -0.02%     
  Complexity     4354     4354              
============================================
  Files           479      479              
  Lines         15856    15856              
  Branches       2175     2175              
============================================
- Hits          11403    11401       -2     
- Misses         3571     3574       +3     
+ Partials        882      881       -1     

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[zhangt2333]

There are two areas that could be improved:

1. This change introduces a string literal "null" to manage code, which could be refined for maintainability.

2. The code should align with the surrounding code to ensure consistency.

A good reference point would be the following line of code just below your change:

Tai-e/src/main/java/pascal/taie/config/Configs.java

Line 103 in 9eb966e

} else if (!Objects.toString(options.get(key)).equals(value)) { // a=b

[cs-cat]

Thanks for your suggestion. I have fixed the commit. @zhangt2333