Check cache value is not null.

[maliming]

Resolve #16776

[codecov[bot]]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (8649bb2) 51.60% compared to head (6653691) 51.63%. Report is 31 commits behind head on prerel-8.1.

Files	Patch %	Lines
...nt.Domain/Volo/Abp/TenantManagement/TenantStore.cs	0.00%	0 Missing and 2 partials :warning:

Additional details and impacted files

@@              Coverage Diff               @@
##           prerel-8.1   #19056      +/-   ##
==============================================
+ Coverage       51.60%   51.63%   +0.03%     
==============================================
  Files            3093     3093              
  Lines           98188    98129      -59     
  Branches         7851     7844       -7     
==============================================
+ Hits            50670    50672       +2     
+ Misses          45967    45907      -60     
+ Partials         1551     1550       -1     

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