DataTree constructor error message says dict even though dict is not accepted

What happened?

When I try to create a DataTree with a dict as the first argument, I get a TypeError:

>>> xr.DataTree(dict())
...
TypeError: data object is not an xarray.Dataset, dict, or None: {}

What did you expect to happen?

A dictionary should be accepted, or the error message should not say that the argument could be a dict.

I suppose this is a leftover from some earlier iteration of the API?

Minimal Complete Verifiable Example

# /// script
# requires-python = ">=3.11"
# dependencies = [
#   "xarray[complete]@git+https://github.com/pydata/xarray.git@main",
# ]
# ///
#
# This script automatically imports the development branch of xarray to check for issues.
# Please delete this header if you have _not_ tested this script with `uv run`!

import xarray as xr
xr.show_versions()
# your reproducer code ...

xr.DataTree(dict())

Steps to reproduce

No response

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.
• Recent environment — the issue occurs with the latest version of xarray and its dependencies.

Relevant log output

File .../xarray/xarray/core/datatree.py:547, in DataTree.__init__(self, dataset, children, name)
    517 def __init__(
    518     self,
    519     dataset: Dataset | Coordinates | None = None,
    520     children: Mapping[str, DataTree] | None = None,
    521     name: str | None = None,
    522 ):
    523     """
    524     Create a single node of a DataTree.
    525 
   (...)    545     DataTree.from_dict
    546     """
--> 547     self._set_node_data(_to_new_dataset(dataset))
    549     # comes after setting node data as this will check for clashes between child names and existing variable names
    550     super().__init__(name=name, children=children)

File .../xarray/xarray/core/datatree.py:143, in _to_new_dataset(data)
    141     ds = Dataset()
    142 else:
--> 143     raise TypeError(f"data object is not an xarray.Dataset, dict, or None: {data}")
    144 return ds

Anything else we need to know?

No response

Environment

Start in xarray/core/datatree.py at DataTree.init and _to_new_dataset, especially the error raised at line 143. Reproduce xr.DataTree(dict()) and update the behavior or message so it no longer contradicts the accepted input types; verify the resulting TypeError or successful construction matches the documented API.