fix(line): handle empty visualMap color stops. close #18066

[rahul37wallst-sudo]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Fix line series rendering when a piecewise visualMap piece has a null bound and produces no gradient color stops.

Fixed issues

• [Bug] Line Charts do not work when lte is set to null #18066: Line charts throw when visualMap.pieces[].lte is set to null.

Details

Before: What was the problem?

When a line series uses a piecewise visualMap with a piece like:

pieces: [{
    lte: null,
    color: '#ff0000'
}]

the visualMap metadata can contain outerColors but no color stops. LineView still tried to read colorStopsInRange[0].coord, causing:

TypeError: Cannot read properties of undefined (reading 'coord')

After: How does it behave after the fixing?

Line series no longer throws for this visualMap configuration.

When there are no in-range color stops, LineView now handles the empty-stop case and returns the available outer color instead of building a gradient from an empty stops array.

A regression test was added for the null-bound piecewise visualMap case.

Validation:

npx jest --config test/ut/jest.config.cjs --coverage=false --runInBand --runTestsByPath test/ut/spec/component/visualMap/nullBound.test.ts
npx jest --config test/ut/jest.config.cjs --coverage=false --runInBand --runTestsByPath test/ut/spec/component/visualMap/setOption.test.ts test/ut/spec/component/visualMap/nullBound.test.ts
npm run checktype

Document Info

One of the following should be checked.

• This PR doesn't relate to document changes
• The document should be updated later
• The document changes have been made in apache/echarts-doc#xxx

Misc

Security Checking

• This PR uses security-sensitive Web APIs.

ZRender Changes

• This PR depends on ZRender changes (ecomfe/zrender#xxx).

Related test cases or examples to use the new APIs

test/ut/spec/component/visualMap/nullBound.test.ts

Merging options

• Please squash the commits into a single one when merging.

Other information

N.A.

[echarts-bot]

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