ansi highlighting not working with theme dark-plus

[chwzr]

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• Read the Contributing Guide.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.

Describe the bug

When using theme dark-plus and language ansi together shiki fails to render anything with following error:

index.js:27 TypeError: Cannot read properties of undefined (reading 'toLowerCase')
    at applyColorReplacements (index.mjs:125:33)
    at eval (index.mjs:460:17)
    at Array.map (<anonymous>)
    at eval (index.mjs:449:52)
    at Array.map (<anonymous>)
    at tokenizeAnsiWithTheme (index.mjs:449:18)
    at _codeToTokensBase (index.mjs:518:16)
    at _codeToTokens (index.mjs:771:18)
    at _codeToHast (index.mjs:1003:53)
    at _codeToHtml (index.mjs:4564:25)
    at Object.codeToHtml (index.mjs:5357:40)
    at _callee9$ (index.mjs:5441:26)
    at tryCatch (regeneratorRuntime.js:45:16)
    at Generator.eval (regeneratorRuntime.js:133:17)
    at Generator.eval [as next] (regeneratorRuntime.js:74:21)
    at asyncGeneratorStep (asyncToGenerator.js:3:24)
    at _next (asyncToGenerator.js:22:9)

Other themes are working fine (e.g. monokai). Included a simple Reproduction Code Sandbox.

Reproduction

https://codesandbox.io/p/sandbox/dark-plus-ansi-8qkpwj?file=%2Fsrc%2Findex.ts%3A1%2C1-20%2C1

Contributes

• I am willing to submit a PR to fix this issue
• I am willing to submit a PR with failing tests

[chwzr]

Figured out that adding optional chaining operator to color.toLowerCase() will make highlighting work.

shiki/packages/core/src/utils.ts

Lines 149 to 151 in b6d40a3

	export function applyColorReplacements(color: string, replacements?: Record<string, string>): string {
	return replacements?.[color.toLowerCase()] || color
	}

[chwzr]

I've implemented a PR for this. Please let me know if this fix is acceptable or if you think there is another way to fix it.