Fix NPE and add additional graceful error handling

[cwperks]

Description

This PR adds graceful error handling in a cache miss scenario where the error is swallowed. Additional tests have been added to verify the new functionality.

Testing

See associated unit tests added

Check List

• New functionality includes testing
• Commits are signed per the DCO using --signoff

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and signing off your commits, please check here.

[stephen-crawford]

Thank you Craig.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 61.44%. Comparing base (bbd43ec) to head (8f4905a).
Report is 680 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2687      +/-   ##
============================================
+ Coverage     61.38%   61.44%   +0.06%     
- Complexity     3383     3385       +2     
============================================
  Files           269      270       +1     
  Lines         18668    18694      +26     
  Branches       3279     3279              
============================================
+ Hits          11459    11487      +28     
+ Misses         5613     5611       -2     
  Partials       1596     1596              

Files with missing lines	Coverage Δ
.../opensearch/security/OpenSearchSecurityPlugin.java	80.16% <100.00%> (+0.12%)	⬆️
...ecurity/support/GuardedSearchOperationWrapper.java	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

[opensearch-trigger-bot]

The backport to 1.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-1.x 1.x
# Navigate to the new working tree
cd .worktrees/backport-1.x
# Create a new branch
git switch --create backport/backport-2687-to-1.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 ed4df62fcb5a3c54869db70dcaf0283472751591
# Push it to GitHub
git push --set-upstream origin backport/backport-2687-to-1.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-1.x

Then, create a pull request where the base branch is 1.x and the compare/head branch is backport/backport-2687-to-1.x.

[opensearch-trigger-bot]

The backport to 1.3 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-1.3 1.3
# Navigate to the new working tree
cd .worktrees/backport-1.3
# Create a new branch
git switch --create backport/backport-2687-to-1.3
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 ed4df62fcb5a3c54869db70dcaf0283472751591
# Push it to GitHub
git push --set-upstream origin backport/backport-2687-to-1.3
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-1.3

Then, create a pull request where the base branch is 1.3 and the compare/head branch is backport/backport-2687-to-1.3.