I'm having difficulty adding a mask function to columns while creating streaming tables using the DLT Python method create_streaming_table() like this but it does not work, the streaming table is created but no column is masked:

def prepare_column_properties_struct(table_contract: dict) -> StructType:
    struct_fields = []

    for column_properties in table_contract["models"]["columns"]:
        column_name = column_properties["name"]
        column_type = column_properties["type"]
        column_nullable = not column_properties["required"]
        column_comment = column_properties["comment"]
        column_mask = column_properties["mask"]

        struct_fields.append(
            StructField(
                name=column_name,
                dataType=parse_data_type(column_type),
                nullable=column_nullable,
                metadata={"comment": column_comment, "mask": "mask_all"},
            )
        )

    return StructType(struct_fields)

dlt.create_streaming_table(
            name="account",
            schema=prepare_column_properties_struct(data_contract),
)

 How do I go about this? Maybe I'm not using the correct metadata key in the StructField? The doc is not helping.