fix: fix PolarisRouterServiceInstanceListSupplier npe with reactive feign

[ShanyouYu-Sean]

PR Type

Bugfix.

Describe what this PR does for and how you did.

fix PolarisRouterServiceInstanceListSupplier npe with reactive feign(a third party dependency)

Adding the issue link (#xxx) if possible.

Note

Checklist

• Add information of this PR to CHANGELOG.md in root of project.
• Add documentation in javadoc or comment below the PR if necessary.

Checklist (Optional)

• Will pull request to branch of 2020.0.
• Will pull request to branch of 2022.0.

[codecov]

Codecov Report

Merging #925 (bc81a3b) into 2020.0 (5b56424) will increase coverage by 0.18%.
The diff coverage is 66.66%.

@@             Coverage Diff              @@
##             2020.0     #925      +/-   ##
============================================
+ Coverage     80.03%   80.21%   +0.18%     
- Complexity     1326     1330       +4     
============================================
  Files           206      206              
  Lines          4502     4503       +1     
  Branches        561      562       +1     
============================================
+ Hits           3603     3612       +9     
+ Misses          557      550       -7     
+ Partials        342      341       -1     

Impacted Files	Coverage Δ
...uter/PolarisRouterServiceInstanceListSupplier.java	90.32% <66.66%> (+13.27%)	⬆️

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[SkyeBeFreeman]

LGTM.