fix ListEdit annotation check (#404)

magicgui/widgets/_concrete.py

@@ -654,8 +654,9 @@ def __init__(
         self.margins = (0, 0, 0, 0)
 
         if not isinstance(value, _Unset):
+            # check type consistency
             types = {type(a) for a in value}
-            if len(types) == 1:
+            if len(types) <= 1:
                 if self._args_type is None:
                     self._args_type = types.pop()
             else:

tests/test_widgets.py

@@ -913,6 +913,18 @@ def f3(x: List[int] = [0]):
     assert f3.x[0].max == 10
     assert f3.x[0].step == 5
 
+    @magicgui
+    def f4(x: List[int] = ()):  # type: ignore
+        pass
+
+    assert type(f4.x) is widgets.ListEdit
+    assert f4.x.annotation == List[int]
+    assert f4.x._args_type is int
+    assert f4.x.value == []
+    f4.x.btn_plus.changed()
+    assert type(f4.x[0]) is widgets.SpinBox
+    assert f4.x.value == [0]
+
 
 def test_tuple_edit():
     """Test TupleEdit."""