Fixed mypy errors in frequencies.py (pandas-dev#47644)

* TST: Added test for consistent type with unique agg pandas-dev#22558

* TST: Added test for consistent type with unique agg pandas-dev#22558

* TST: Moved and restructured test pandas-dev#22558

* TYP: Fixed mypy issues in frequencies

* TYP: Removed accidental inclusion

Co-authored-by: Steven Rotondo <[email protected]>

Author: srotondo

pandas/tseries/frequencies.py

@@ -394,11 +394,11 @@ def _get_annual_rule(self) -> str | None:
             return None
 
         pos_check = self.month_position_check()
-        #  error: Argument 1 to "get" of "dict" has incompatible type
-        # "Optional[str]"; expected "str"
-        return {"cs": "AS", "bs": "BAS", "ce": "A", "be": "BA"}.get(
-            pos_check  # type: ignore[arg-type]
-        )
+
+        if pos_check is None:
+            return None
+        else:
+            return {"cs": "AS", "bs": "BAS", "ce": "A", "be": "BA"}.get(pos_check)
 
     def _get_quarterly_rule(self) -> str | None:
         if len(self.mdiffs) > 1:
@@ -408,21 +408,21 @@ def _get_quarterly_rule(self) -> str | None:
             return None
 
         pos_check = self.month_position_check()
-        # error: Argument 1 to "get" of "dict" has incompatible type
-        # "Optional[str]"; expected "str"
-        return {"cs": "QS", "bs": "BQS", "ce": "Q", "be": "BQ"}.get(
-            pos_check  # type: ignore[arg-type]
-        )
+
+        if pos_check is None:
+            return None
+        else:
+            return {"cs": "QS", "bs": "BQS", "ce": "Q", "be": "BQ"}.get(pos_check)
 
     def _get_monthly_rule(self) -> str | None:
         if len(self.mdiffs) > 1:
             return None
         pos_check = self.month_position_check()
-        # error: Argument 1 to "get" of "dict" has incompatible type
-        # "Optional[str]"; expected "str"
-        return {"cs": "MS", "bs": "BMS", "ce": "M", "be": "BM"}.get(
-            pos_check  # type: ignore[arg-type]
-        )
+
+        if pos_check is None:
+            return None
+        else:
+            return {"cs": "MS", "bs": "BMS", "ce": "M", "be": "BM"}.get(pos_check)
 
     def _is_business_daily(self) -> bool:
         # quick check: cannot be business daily