Fix failures when performing binary operations on DataFrames with emp…

…ty columns (#8452)

Closes #8434

Authors:
  - https://github.com/ChrisJar

Approvers:
  - GALI PREM SAGAR (https://github.com/galipremsagar)
  - Charles Blackmon-Luca (https://github.com/charlesbluca)

URL: #8452

python/cudf/cudf/core/frame.py

@@ -3401,6 +3401,30 @@ def _colwise_binop(
             col,
             (left_column, right_column, reflect, fill_value),
         ) in operands.items():
+
+            # Handle object columns that are empty or
+            # all nulls when performing binary operations
+            if (
+                left_column.dtype == "object"
+                and left_column.null_count == len(left_column)
+                and fill_value is None
+            ):
+                if fn in (
+                    "add",
+                    "sub",
+                    "mul",
+                    "mod",
+                    "pow",
+                    "truediv",
+                    "floordiv",
+                ):
+                    output[col] = left_column
+                elif fn in ("eq", "lt", "le", "gt", "ge"):
+                    output[col] = left_column.notnull()
+                elif fn == "ne":
+                    output[col] = left_column.isnull()
+                continue
+
             if right_column is cudf.NA:
                 right_column = cudf.Scalar(
                     right_column, dtype=left_column.dtype

python/cudf/cudf/tests/test_binops.py

@@ -37,6 +37,15 @@
     operator.pow,
 ]
 
+_binops_compare = [
+    operator.eq,
+    operator.ne,
+    operator.lt,
+    operator.le,
+    operator.gt,
+    operator.ge,
+]
+
 
 @pytest.mark.parametrize("obj_class", ["Series", "Index"])
 @pytest.mark.parametrize("binop", _binops)
@@ -2888,3 +2897,19 @@ def test_binops_non_cudf_types(obj_class, binop, other_type):
     lhs = obj_class(data)
     rhs = other_type(data)
     assert cp.all((binop(lhs, rhs) == binop(lhs, lhs)).values)
+
+
+@pytest.mark.parametrize("binop", _binops + _binops_compare)
+@pytest.mark.parametrize("data", [None, [-9, 7], [5, -2], [12, 18]])
+@pytest.mark.parametrize("scalar", [1, 3, 12, np.nan])
+def test_empty_column(binop, data, scalar):
+    gdf = cudf.DataFrame(columns=["a", "b"])
+    if data is not None:
+        gdf["a"] = data
+
+    pdf = gdf.to_pandas()
+
+    got = binop(gdf, scalar)
+    expected = binop(pdf, scalar)
+
+    utils.assert_eq(expected, got)