Cannot pass empty dict as argument to function in client.submit/client.map

[wence-]

Describe the issue:

Since the merge #8920 (and dask/dask#11477) it looks like one cannot pass empty dictionaries as arguments to functions through client.submit or client.map

Minimal Complete Verifiable Example:

import distributed

client = distributed.Client()

def identity(*args, **kwargs):
    return args, kwargs

client.submit(identity, {}).result() # ValueError: Dict needs at least one argument

client.submit(identity, x={}).result() # ValueError: Dict needs at least one argument

client.submit(identity, x=None).result() # Fine.

client.map(identity, [None], kw={"foo": {"bar": {}}}) # ValueError: Dict needs at least one argument

This patch in dask allows the above examples to complete for me:

diff --git a/dask/_task_spec.py b/dask/_task_spec.py
index 82b896b6..c67318fb 100644
--- a/dask/_task_spec.py
+++ b/dask/_task_spec.py
@@ -728,8 +728,6 @@ class Dict(NestedContainer):
             if len(args) > 1:
                 raise ValueError("Dict can only take one positional argument")
             kwargs = args[0]
-        elif not kwargs:
-            raise ValueError("Dict needs at least one argument")
         super().__init__(
             *(Tuple(*it) for it in kwargs.items()), _dependencies=_dependencies
         )

However, I am not sure if that is incorrectly relaxing an invariant that should be upheld by the Dict class (namely that it has at least one entry).

Environment:

• Dask version: 2024.11.2+23.g0f3e5ff6
• Python version: 3.12