fix: Fix invalid state causing migration 88 to fail

[Gudahtt]

Description

We have found evidence that migration 88 is failing for some users due to a null key in the TokensController.allTokens state. The migration has been updated to delete any invalid null-keys prior to migrating it, preventing the error.

Related issues

Fixes #25938

Manual testing steps

The unit tests demonstrate the affected scenario fairly well. We addressed the "null key" case for a variety of different parts of state, but specifically the one we are seeing in prod is the allTokens state having a null key.

Screenshots/Recordings

N/A

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Extension Coding Standards.
• I've completed the PR template to the best of my ability
• I’ve included tests if applicable
• I’ve documented my code using JSDoc format if applicable
• I’ve applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

[Gudahtt]

Strongly recommend using "Hide whitespace" to view this diff, it's only 38 lines with that enabled.

[sonarcloud]

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 SonarCloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.14%. Comparing base (b3c2323) to head (47a2415).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop   #26397      +/-   ##
===========================================
+ Coverage    70.13%   70.14%   +0.01%     
===========================================
  Files         1435     1435              
  Lines        50309    50327      +18     
  Branches     13897    13915      +18     
===========================================
+ Hits         35283    35301      +18     
  Misses       15026    15026              

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[metamaskbot]

Builds ready [47a2415]

• builds: chrome, firefox
• builds (beta): chrome
• builds (flask): chrome, firefox
• builds (MMI): chrome, firefox
• builds (test): chrome, firefox
• builds (test-flask): chrome, firefox
• build viz: Build System
• mv3: Background Module Init Stats
• mv3: UI Init Stats
• mv3: Module Load Stats
• mv3: Bundle Size Stats
• mv2: E2e Actions Stats
• code coverage: Report
• storybook: Storybook
• typescript migration: Dashboard
• all artifacts
• bundle viz:

  • background: 0, 1, 2, 3, 4, 5, 6
  • common: 0, 1, 10, 2, 3, 4, 5, 6, 7, 8, 9
  • content-script: 0
  • offscreen: 0
  • ui: 0, 1, 10, 11, 2, 3, 4, 5, 6, 7, 8, 9

Page Load Metrics (66 ± 7 ms)

Platform	Page	Metric	Min (ms)	Max (ms)	Average (ms)	StandardDeviation (ms)	MarginOfError (ms)
Chrome	Home	firstPaint	75	123	95	15	7
		domContentLoaded	9	51	21	11	5
		load	41	96	66	15	7
		domInteractive	9	51	21	11	5

Bundle size diffs [🚨 Warning! Bundle size has increased!]

• background: 72 Bytes (0.00%)
• ui: 0 Bytes (0.00%)
• common: 0 Bytes (0.00%)

[Gudahtt]

Pretty sure Object.keys would always return undefined as a string literal, do we shouldn't need this condition. But it was already there, so I left it to minimize changes.

I confirmed that using null here didn't work, I needed to check for the string 'null'.