[mattermost] Clean up null handling and Painless scripts

[chrisberkhout]

Proposed commit message

[mattermost] Clean up null handling and Painless scripts (#)

- Remove redundant null-safe operator.
- Remove redundant null-safe access to ctx.
- Reformat Painless scripts.
- Merge if statements with else where conditions are mutually exclusive.
- Combine 'not null and is/not value' checks.
- Combine 'is null or not contains' checks.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
• I have verified that Kibana version constraints are current according to guidelines.

Related issues

• Relates Incorrect null handling in if conditions and elsewhere #8646

[elasticmachine]

🚀 Benchmarks report

To see the full report comment with /test benchmark fullreport

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 85f3d15

History

• 💚 Build #9015 succeeded 7d5917a

cc @chrisberkhout

[elastic-sonarqube]

Quality Gate failed

Failed conditions

54.5% Coverage on New Code (required ≥ 80%)

See analysis details on SonarQube

[elasticmachine]

Package mattermost - 1.17.3 containing this change is available at https://epr.elastic.co/search?package=mattermost