fix null query filter conversion from sigma to query string query

[eirsep]

Description

Null filters in Sigma rules are not translated properly to queries leading to False Positives and broken detections.
They are being treated as term query to match field to value "null" instead of checking if value is nullable or field not exists.
This change fixes the query string query for the null filter conversion from sigma to backend search query

Issues Resolved

#683

Check List

• New functionality includes testing.
  • All tests pass
• New functionality has been documented.
  • New functionality has javadoc added
• 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.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (43040d6) 24.72% compared to head (bb591fe) 24.76%.

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #722      +/-   ##
============================================
+ Coverage     24.72%   24.76%   +0.03%     
- Complexity     1017     1021       +4     
============================================
  Files           275      275              
  Lines         12663    12663              
  Branches       1389     1389              
============================================
+ Hits           3131     3136       +5     
+ Misses         9264     9261       -3     
+ Partials        268      266       -2     

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[opensearch-trigger-bot]

The backport to 2.10 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-2.10 2.10
# Navigate to the new working tree
cd .worktrees/backport-2.10
# Create a new branch
git switch --create backport/backport-722-to-2.10
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 a59a014467bf1dde7cb40f9d8012545a315cddff
# Push it to GitHub
git push --set-upstream origin backport/backport-722-to-2.10
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.10

Then, create a pull request where the base branch is 2.10 and the compare/head branch is backport/backport-722-to-2.10.

[opensearch-trigger-bot]

The backport to 2.8 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-2.8 2.8
# Navigate to the new working tree
cd .worktrees/backport-2.8
# Create a new branch
git switch --create backport/backport-722-to-2.8
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 a59a014467bf1dde7cb40f9d8012545a315cddff
# Push it to GitHub
git push --set-upstream origin backport/backport-722-to-2.8
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.8

Then, create a pull request where the base branch is 2.8 and the compare/head branch is backport/backport-722-to-2.8.

[opensearch-trigger-bot]

The backport to 2.9 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-2.9 2.9
# Navigate to the new working tree
cd .worktrees/backport-2.9
# Create a new branch
git switch --create backport/backport-722-to-2.9
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 a59a014467bf1dde7cb40f9d8012545a315cddff
# Push it to GitHub
git push --set-upstream origin backport/backport-722-to-2.9
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.9

Then, create a pull request where the base branch is 2.9 and the compare/head branch is backport/backport-722-to-2.9.

[opensearch-trigger-bot]

The backport to 2.6 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-2.6 2.6
# Navigate to the new working tree
cd .worktrees/backport-2.6
# Create a new branch
git switch --create backport/backport-722-to-2.6
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 a59a014467bf1dde7cb40f9d8012545a315cddff
# Push it to GitHub
git push --set-upstream origin backport/backport-722-to-2.6
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.6

Then, create a pull request where the base branch is 2.6 and the compare/head branch is backport/backport-722-to-2.6.

[opensearch-trigger-bot]

The backport to 2.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-2.x 2.x
# Navigate to the new working tree
cd .worktrees/backport-2.x
# Create a new branch
git switch --create backport/backport-722-to-2.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 a59a014467bf1dde7cb40f9d8012545a315cddff
# Push it to GitHub
git push --set-upstream origin backport/backport-722-to-2.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.x

Then, create a pull request where the base branch is 2.x and the compare/head branch is backport/backport-722-to-2.x.

[opensearch-trigger-bot]

The backport to 2.11 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-2.11 2.11
# Navigate to the new working tree
cd .worktrees/backport-2.11
# Create a new branch
git switch --create backport/backport-722-to-2.11
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 a59a014467bf1dde7cb40f9d8012545a315cddff
# Push it to GitHub
git push --set-upstream origin backport/backport-722-to-2.11
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.11

Then, create a pull request where the base branch is 2.11 and the compare/head branch is backport/backport-722-to-2.11.

[opensearch-trigger-bot]

The backport to 2.7 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-2.7 2.7
# Navigate to the new working tree
cd .worktrees/backport-2.7
# Create a new branch
git switch --create backport/backport-722-to-2.7
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 a59a014467bf1dde7cb40f9d8012545a315cddff
# Push it to GitHub
git push --set-upstream origin backport/backport-722-to-2.7
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.7

Then, create a pull request where the base branch is 2.7 and the compare/head branch is backport/backport-722-to-2.7.

[opensearch-trigger-bot]

The backport to 2.5 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-2.5 2.5
# Navigate to the new working tree
cd .worktrees/backport-2.5
# Create a new branch
git switch --create backport/backport-722-to-2.5
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 a59a014467bf1dde7cb40f9d8012545a315cddff
# Push it to GitHub
git push --set-upstream origin backport/backport-722-to-2.5
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.5

Then, create a pull request where the base branch is 2.5 and the compare/head branch is backport/backport-722-to-2.5.