Don't let Column.name be None (#223)

* unnunnable-ify name

* allow default empty string name

* optionality

* fixup

spec/API_specification/dataframe_api/__init__.py

@@ -63,7 +63,7 @@ def concat(dataframes: Sequence[DataFrame]) -> DataFrame:
     """
     ...
 
-def column_from_sequence(sequence: Sequence[Any], *, name: str | None, dtype: Any) -> Column[Any]:
+def column_from_sequence(sequence: Sequence[Any], *, dtype: Any, name: str = '') -> Column[Any]:
     """
     Construct Column from sequence of elements.
 
@@ -109,7 +109,7 @@ def dataframe_from_dict(data: Mapping[str, Column[Any]]) -> DataFrame:
     ...
 
 
-def column_from_1d_array(array: Any, *, name: str, dtype: Any) -> Column[Any]:
+def column_from_1d_array(array: Any, *, dtype: Any, name: str = '') -> Column[Any]:
     """
     Construct Column from 1D array.
 
@@ -123,7 +123,7 @@ def column_from_1d_array(array: Any, *, name: str, dtype: Any) -> Column[Any]:
     ----------
     array : array
         array-API compliant 1D array
-    name : str
+    name : str, optional
         Name to give columns.
     dtype : DType
         Dtype of column.

spec/API_specification/dataframe_api/column_object.py

@@ -47,7 +47,7 @@ def column(self) -> Any:
         ...
 
     @property
-    def name(self) -> str | None:
+    def name(self) -> str:
         """Return name of column."""
 
     def __len__(self) -> int:
@@ -724,7 +724,7 @@ def to_array_object(self, dtype: Any) -> Any:
         ``array-api-compat`` package to convert it to a Standard-compliant array.
         """
 
-    def rename(self, name: str | None) -> Column[DType]:
+    def rename(self, name: str) -> Column[DType]:
         """
         Rename column.