BUG: df_empty.convert_dtypes() with pyarrow backend

Author: mroeschke

pandas/core/arrays/arrow/array.py

@@ -137,15 +137,17 @@ def to_pyarrow_type(
     Convert dtype to a pyarrow type instance.
     """
     if isinstance(dtype, ArrowDtype):
-        pa_dtype = dtype.pyarrow_dtype
+        return dtype.pyarrow_dtype
     elif isinstance(dtype, pa.DataType):
-        pa_dtype = dtype
+        return dtype
     elif dtype:
-        # Accepts python types too
-        pa_dtype = pa.from_numpy_dtype(dtype)
-    else:
-        pa_dtype = None
-    return pa_dtype
+        try:
+            # Accepts python types too
+            # Doesn't handle all numpy types
+            return pa.from_numpy_dtype(dtype)
+        except pa.ArrowNotImplementedError:
+            pass
+    return None
 
 
 class ArrowExtensionArray(OpsMixin, ExtensionArray):

pandas/tests/frame/methods/test_convert_dtypes.py

@@ -120,3 +120,10 @@ def test_pyarrow_dtype_backend_from_pandas_nullable(self):
             }
         )
         tm.assert_frame_equal(result, expected)
+
+    def test_pyarrow_dtype_empty_object(self):
+        # GH 50970
+        expected = pd.DataFrame(columns=[0])
+        with pd.option_context("mode.dtype_backend", "pyarrow"):
+            result = expected.convert_dtypes()
+        tm.assert_frame_equal(result, expected)