What happened?

Calling xr.DataArray.diff with a non-existing dimension does not raise an exception.

What did you expect to happen?

An exception to be raised.

Minimal Complete Verifiable Example

import xarray as xr; import numpy as np; xr.DataArray(np.arange(10),dims=('a',)).diff('b')

MVCE confirmation

• Minimal example — the example is as focused as reasonably possible to demonstrate the underlying issue in xarray.
• Complete example — the example is self-contained, including all data and the text of any traceback.
• Verifiable example — the example copy & pastes into an IPython prompt or Binder notebook, returning the result.
• New issue — a search of GitHub Issues suggests this is not a duplicate.

Relevant log output

No response

Anything else we need to know?

No response

Environment