Error palette not exported to JSON

[tipa]

Describe the bug When exporting to JSON, the error palette is missing, even though it is displayed on the theme builder

To Reproduce Steps to reproduce the behavior:

1. Go to https://material-foundation.github.io/material-theme-builder/
2. Click on the export button on the top right
3. Click "Export" -> "Material Theme (JSON)"
4. Open downloaded JSON
5. The JSON contains the "primary", "secondardy", "tertiary", "neutral" & "neutral-variant" palette, but not the "error" palette

Expected behavior The JSON contains the error palette

Screenshots

Additional context I want to programmatically generate my Android themes based on the JSON, mostly because exporting the Android XML is bugged. See these issues for context: https://github.com/material-foundation/material-theme-builder/issues/308, https://github.com/material-foundation/material-theme-builder/issues/313