fix: guard against nil spec.replicas in deployment analyzer

[anxkhn]

Description

The Deployment analyzer dereferences *deployment.Spec.Replicas without a nil
check. Spec.Replicas is a *int32; although the API server usually defaults
it to 1, a Deployment object whose spec.replicas is explicitly unset (nil)
panics the analyze run with a nil pointer dereference at
pkg/analyzer/deployment.go:57.

This guards the comparison with a nil check, mirroring the sibling StatefulSet
analyzer (pkg/analyzer/statefulset.go:97), which already checks
Spec.Replicas != nil before dereferencing. The single guard also protects the
subsequent *deployment.Spec.Replicas reads on lines 58, 62, and 79, since they
only run inside the guarded block.

Added a regression test, TestDeploymentAnalyzerNilReplicas, that analyzes a
Deployment with nil spec.replicas and asserts Analyze returns no results and
does not panic.

Checks

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

Additional Information

No behavior change for Deployments that set spec.replicas (the overwhelming
common case, since the API server defaults it). The only difference is that a
Deployment with an explicitly-unset replicas field is now skipped instead of
crashing the analyzer.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 45.95%. Comparing base (173e4dc) to head (beca44d).
⚠️ Report is 253 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1683       +/-   ##
===========================================
+ Coverage   34.76%   45.95%   +11.18%     
===========================================
  Files          94      121       +27     
  Lines        6342     7533     +1191     
===========================================
+ Hits         2205     3462     +1257     
+ Misses       4046     3838      -208     
- Partials       91      233      +142     

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[AlexsJones]

Reviewed the diff — this is a correct, minimal fix. ✅

• pkg/analyzer/deployment.go:57 did dereference *deployment.Spec.Replicas unconditionally, and Spec.Replicas is a *int32, so a Deployment with an explicitly-unset spec.replicas would panic the analyze run. Real bug.
• The guard deployment.Spec.Replicas != nil && … short-circuits before the deref, and every other *deployment.Spec.Replicas read (the Status.Replicas > *Spec.Replicas comparison and both failure messages) lives inside that same block, so the single guard covers all of them.
• It mirrors the sibling StatefulSetAnalyzer, which already uses sts.Spec.Replicas != nil && *(sts.Spec.Replicas) != … — so this keeps the two analyzers consistent.
• TestDeploymentAnalyzerNilReplicas is a proper regression test: it feeds a nil-replicas Deployment and asserts no panic / zero results. CI (build, golangci-lint, validate, codecov) is green.

No behavior change for the common case where spec.replicas is set. Recommending this for merge — over to @AlexsJones for the final call.

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