Avoid nan_as_null op if nan_count is 0 (#10082)

This PR avoid make `nan_as_null` a no-op if `nan_count` is 0, i.e., there are no nulls present.

Authors:
  - GALI PREM SAGAR (https://github.com/galipremsagar)

Approvers:
  - https://github.com/brandon-b-miller

URL: #10082

python/cudf/cudf/core/column/column.py

@@ -1213,11 +1213,7 @@ def corr(self, other: ColumnBase):
         )
 
     def nans_to_nulls(self: T) -> T:
-        # Only floats can contain nan.
-        if self.dtype.kind != "f":
-            return self
-        newmask = libcudf.transform.nans_to_nulls(self)
-        return self.set_mask(newmask)
+        return self
 
     def _process_for_reduction(
         self, skipna: bool = None, min_count: int = 0

python/cudf/cudf/core/column/numerical.py

@@ -217,6 +217,13 @@ def binary_operator(
         lhs, rhs = (self, rhs) if not reflect else (rhs, self)
         return libcudf.binaryop.binaryop(lhs, rhs, binop, out_dtype)
 
+    def nans_to_nulls(self: NumericalColumn) -> NumericalColumn:
+        # Only floats can contain nan.
+        if self.dtype.kind != "f" or self.nan_count == 0:
+            return self
+        newmask = libcudf.transform.nans_to_nulls(self)
+        return self.set_mask(newmask)
+
     def normalize_binop_value(
         self, other: ScalarLike
     ) -> Union[ColumnBase, ScalarLike]: