Remove redundant null declaration

[rlazo]

Since the constructor is private, and the builder sets it to null if missing, this declaration is actually redundant.

b/368368914

[github-actions]

📝 PRs merging into main branch

Our main branch should always be in a releasable state. If you are working on a larger change, or if you don't want this change to see the light of the day just yet, consider using a feature branch first, and only merge into the main branch when the code complete and ready to be released.

[google-oss-bot]

	1 Warning
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Generated by 🚫 Danger

[google-oss-bot]

Coverage Report ¹

Affected Products

No changes between base commit (3c842c7) and merge commit (c94232c).

Test Logs

• Merge (c94232c): https://github.com/firebase/firebase-android-sdk/actions/runs/10947493114

1. https://storage.googleapis.com/firebase-sdk-metric-reports/mkjA5mZJxO.html

[github-actions]

Unit Test Results

  16 files  ±0    16 suites  ±0   15s ⏱️ ±0s
108 tests ±0  108 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
216 runs  ±0  216 ✔️ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 867e517. ± Comparison against base commit 3c842c7.

[google-oss-bot]

Size Report ¹

Affected Products

• firebase-vertexai

  Type	Base (3c842c7)	Merge (c94232c)	Diff
  aar	489 kB	489 kB	-68 B (-0.0%)
  apk (release)	9.30 MB	9.30 MB	-140 B (-0.0%)

Test Logs

• Base (3c842c7): https://github.com/firebase/firebase-android-sdk/actions/runs/10947201094
• Merge (c94232c): https://github.com/firebase/firebase-android-sdk/actions/runs/10947493114

1. https://storage.googleapis.com/firebase-sdk-metric-reports/NDS2kIYEDx.html