setting dtype instead of asserting warnings in most tests

Author: SaturnFromTitan

pandas/core/groupby/generic.py

@@ -1182,9 +1182,17 @@ def first_not_none(values):
             if v is None:
                 return DataFrame()
             elif isinstance(v, NDFrame):
+
+                # this is to silence a FutureWarning
+                # TODO: Remove when default dtype of empty Series is object
+                kwargs = v._construct_axes_dict()
+                if v._constructor is Series:
+                    is_empty = "data" not in kwargs or not kwargs["data"]
+                    if "dtype" not in kwargs and is_empty:
+                        kwargs["dtype"] = object
+
                 values = [
-                    x if x is not None else v._constructor(**v._construct_axes_dict())
-                    for x in values
+                    x if (x is not None) else v._constructor(**kwargs) for x in values
                 ]
 
             v = values[0]