fix: avoid NPE when closing terminal with null masterOutput

[gnodet]

Fixes #1796

Summary

• Add null guards for masterOutput in LineDisciplineTerminal.FilteringOutputStream.flush() and close() to prevent NPE when closing a terminal created with system(false) and no output stream
• Also guard processOutputByte(), processInputByte(), and processInputBytes() for completeness
• Add test verifying that closing an ExternalTerminal with null masterOutput does not throw

Summary by CodeRabbit

Release Notes

• Bug Fixes

  • Improved terminal stability by adding defensive null checks to output processing and stream closure operations, preventing potential exceptions when output streams are unavailable.

• Tests

  • Added new test case to verify the terminal closes gracefully in edge-case scenarios.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: d13d5855-1f29-4304-9fe1-4c0e9ef94df9

📥 Commits

Reviewing files that changed from the base of the PR and between eeb053e and 8c8975b.

📒 Files selected for processing (2)

• terminal/src/main/java/org/jline/terminal/impl/LineDisciplineTerminal.java
• terminal/src/test/java/org/jline/terminal/impl/NullOutputCloseTest.java

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📝 Walkthrough

Walkthrough

Fixed a NullPointerException when closing a terminal with a null master output stream by adding null checks to guard flush and close operations in LineDisciplineTerminal and its FilteringOutputStream inner class. Includes a test verifying closure completes without exceptions.

Changes

Cohort / File(s)	Summary
Null Safety Guards terminal/src/main/java/org/jline/terminal/impl/LineDisciplineTerminal.java	Added null checks for masterOutput in input-driven flushes, output byte processing, and FilteringOutputStream's flush() and close() methods to prevent NPE during terminal closure when master output is null.
Test Coverage terminal/src/test/java/org/jline/terminal/impl/NullOutputCloseTest.java	New JUnit 5 test that verifies ExternalTerminal.close() completes without throwing exceptions when master output is null.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐰 A hop, a fix, a null to tame,
No more crashes in the closing game,
With guards in place, the stream runs free,
Now terminals close so happily! 🎉

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and accurately describes the main change: adding null guards to prevent NullPointerException when closing a terminal with null masterOutput.
Linked Issues check	✅ Passed	The PR fully addresses issue #1796 by adding null guards in FilteringOutputStream.flush() and close() methods, plus guards in related methods, and includes a test verifying the fix works.
Out of Scope Changes check	✅ Passed	All changes are directly within scope: null guards in LineDisciplineTerminal.java and a test in NullOutputCloseTest.java both address the linked issue requirement.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch ci-issue-1796

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud