[windows] prevent pipeline script error

[leehinman]

What does this PR do?

Prevents pipeline script error in windows integration

• prevent creating new HashMap with null
• improve error.message

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.
  - [ ] If I'm introducing a new feature, I have modified the Kibana version constraint in my package's manifest.yml file to point to the latest Elastic stack release (e.g. ^7.13.0).

How to test this PR locally

elastic-package test pipeline

Related issues

• Relates [system] error.message for java.util.Map.size() because "m" is null #1789

[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[elasticmachine]

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Build stats

• Start Time: 2021-10-06T01:55:14.106+0000

• Duration: 17 min 29 sec

• Commit: 2a15657

Test stats 🧪

Test	Results
Failed	0
Passed	126
Skipped	0
Total	126

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