do not assign default value to sparse dtypes since that knowledge is …

…already baked-in (#1278, #1370)

Signed-off-by: Derin Walters <[email protected]>

pandera/backends/pandas/array.py

@@ -325,9 +325,10 @@ def run_checks(self, check_obj, schema) -> List[CoreCheckResult]:
 
     def set_default(self, check_obj, schema):
         """Sets the ``schema.default`` value on the ``check_obj``"""
-        if is_field(check_obj):
+        # Ignore sparse dtype as it can't assign default value directly
+        if is_field(check_obj) and not isinstance(check_obj.dtype, pd.SparseDtype):
             check_obj.fillna(schema.default, inplace=True)
-        else:
+        elif not is_field(check_obj) and not isinstance(check_obj[schema.name].dtype, pd.SparseDtype):
             check_obj[schema.name].fillna(schema.default, inplace=True)
 
         return check_obj