a '{kind}' rolling column needs a positive window span (a count of rows, or a time span in ms or 'minutes'); it had none, so the column reported null.

Warnings reference › grid.rolling.window:*:*

Identifier

grid.rolling.window:*:*

Raised by

The grid (core)

Since

1.29.0

What happened

The rolling window has no usable size: the span is missing, zero, negative or unparseable. There is no window to reduce over, so the column reports null for every row rather than inventing a default width.

The fix

Give the window a positive span - a row count, or a time span in milliseconds (or minutes).

The smallest fix

rolling: { kind: 'mean', of: 'price', orderBy: 'at', window: { kind: 'time', minutes: 15 } }

Reference

Covered in full at the API reference.