def _remove_backslash_line_continuation_chars(
        line: Line, string_indices: list[int]
    ) -> TResult[Line]:
        """
        Merge strings that were split across multiple lines using
        line-continuation backslashes.

        Returns:
            Ok(new_line), if @line contains backslash line-continuation
            characters.
                OR
            Err(CannotTransform), otherwise.
        """
        LL = line.leaves

        indices_to_transform = []
        for string_idx in string_indices:
            string_leaf = LL[string_idx]
            if (
                string_leaf.type == token.STRING
                and "\\\n" in string_leaf.value
                and not has_triple_quotes(string_leaf.value)
            ):
                indices_to_transform.append(string_idx)

        if not indices_to_transform:
            return TErr(
                "Found no string leaves that contain backslash line continuation"
                " characters."
            )

        new_line = line.clone()
        new_line.comments = line.comments.copy()
        append_leaves(new_line, line, LL)

        for string_idx in indices_to_transform:
            new_string_leaf = new_line.leaves[string_idx]
            new_string_leaf.value = new_string_leaf.value.replace("\\\n", "")

        return Ok(new_line)

        Merge strings that were split across multiple lines using
        line-continuation backslashes.

        Returns:
            Ok(new_line), if @line contains backslash line-continuation
            characters.
                OR
            Err(CannotTransform), otherwise.
        
src/black/trans.py