fix(line): fix areaStyle render error when dimension name is empty string

[Justin-ZS]

Brief Information

This pull request is in the type of:

• bug fixing
• new feature
• others

What does this PR do?

Fix line area rendering issue when dataset dimension name is empty string.

Fixed issues

• [Bug] Wrong line area when dataset.dimension[].name is empty string #20756

Details

Before: What was the problem?

When dataset.dimensions[].name is set to an empty string "", the line chart with areaStyle renders incorrectly.

Root cause: In getStackedOnPoints function, empty string dimension name fails truthiness check:

if (!dataCoordInfo.valueDim) {  // Empty string "" is falsy
    return [];
}

This causes the function to return empty stackedOnPoints array, breaking area rendering.

After: How does it behave after the fixing?

Changed the check to only reject null/undefined values:

if (dataCoordInfo.valueDim == null) {  // Only reject null/undefined
    return [];
}

Empty string dimension names are now treated as valid dimension names for area rendering.

Document Info

• 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

ZRender Changes

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

Others

Merging options

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

[echarts-bot]

Thanks for your contribution!
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[Justin-ZS]

@Ovilia Could you help to review the PR? Thanks!

[github-actions]

The changes brought by this PR can be previewed at: https://echarts.apache.org/examples/editor?version=PR-21219@2e42179

[Ovilia]

Thanks for your contribution!

[echarts-bot]

Congratulations! Your PR has been merged. Thanks for your contribution! 👍