fix #7764

[chess99]

No description provided.

[Ovilia]

@chess99 Thanks for your contribution!

Now you are one of the ECharts contributors. Since we joined Apache group, you need to assign ICLA for your first PR.
Please fill in the PDF and print it, then sign on it and send the scanned file to dev@echarts.apache.org and oviliazhang@gmail.com.
This may be a little tricky, and sorry for the trouble. This is required for the first time your commit is merged in. If you refused, your commit will be backed off.

And are you interested in being an ECharts committer? This has more restrict rules than contributors. Committers are those who contribute more frequently and play more important roles on ECharts project.

After being a committer:

• You can have write access to the ECharts code
• You can mange issues (add tags, assign to someone, ...)
• You can discuss about features with us committers more frequently with Email
• You name and personal page link will be displayed at ECharts Website About page
• See this for more information

If you are interested, here's what you can do:

• Subscribe our mailing list by send an email to dev-subscribe@echarts.apache.org
• When you want to discuss with us about something, send email to dev@echarts.apache.org
• Help others by replying issues regularly
• Make more useful pull requests (fix bugs or make enhancement in issues)

And you will be invited to be a committer when we think your contribution and knowledge of ECharts project is enough. We are looking forward to this! 😃