fix:fix NPE when rate-limiting with null value.

[SkyeBeFreeman]

No description provided.

[shedfreewu]

OK.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 19.78%. Comparing base (33a341a) to head (bea0b97).
⚠️ Report is 1 commits behind head on release/2.1.0.x.

Files with missing lines	Patch %	Lines
...ncent/polaris/ratelimit/client/flow/QuotaFlow.java	0.00%	2 Missing ⚠️

Additional details and impacted files

@@                  Coverage Diff                  @@
##             release/2.1.0.x     #669      +/-   ##
=====================================================
+ Coverage              19.77%   19.78%   +0.01%     
  Complexity               941      941              
=====================================================
  Files                    373      373              
  Lines                  15568    15570       +2     
  Branches                1995     1996       +1     
=====================================================
+ Hits                    3078     3081       +3     
+ Misses                 12105    12103       -2     
- Partials                 385      386       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.