fix: Make sure not to crash user search api when search service returns empty dict

[verdan]

Summary of Changes

With the changes introduces in this PR: amundsen-io/amundsensearchlibrary#111 , if your user index feature is not implemented in the search i.e., has pass, then the frontend does not work and crashes. This PR will fix this issue.

Tests

Added the corresponding test case!

Documentation

N/A

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[codecov-commenter]

Codecov Report

Merging #503 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #503   +/-   ##
=======================================
  Coverage   81.02%   81.02%           
=======================================
  Files         226      226           
  Lines        5638     5638           
  Branches      666      666           
=======================================
  Hits         4568     4568           
  Misses       1004     1004           
  Partials       66       66           

Impacted Files	Coverage Δ
amundsen_application/api/search/v0.py	95.86% <100.00%> (ø)

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[verdan]

@feng-tao can you please review. This PR fixes a crash introduced in the search library.

[feng-tao]

thanks @verdan

[feng-tao]

@verdan , qq: is it correct that ING has indexed user info into Atlas but didn't implement the search function for user entity?

[verdan]

@feng-tao that is true. We still need to implement the user related features for Atlas. The only reason we enabled the userIndex is to enable the User Profile. But yes, we will be implementing all these features over the time.