Serialize a table of string values

PackStrings.sql

/*
CREATE TYPE [dbo].[StringArray] AS TABLE (
     ElementNumber INT IDENTITY(1,1)
    ,[Element] NVARCHAR(MAX)
)
*/

CREATE FUNCTION [dbo].[PackStrings]
(
     @original [dbo].[StringArray] READONLY
    ,@delimiter NCHAR(1)
    ,@zed NCHAR(1)
    ,@escape NCHAR(1)
) RETURNS NVARCHAR(MAX) AS BEGIN
    DECLARE @next INT;
    DECLARE @pos INT;
    DECLARE @sb NVARCHAR(MAX) = '';
    DECLARE @sb_ NVARCHAR(MAX) = '';
    DECLARE @element NVARCHAR(MAX);
    
    -- Special characters must be distinct.
    IF ( (@delimiter = @escape) OR 
            (@zed = @escape) OR 
            (@delimiter = @zed) )
        RETURN CAST('Special characters must be distinct.' AS INT);  -- (Can't throw or raiserror in a function)

    -- Null string return a null array -- custom table type cannot be null value
    -- IF (@original IS NULL)
    --    RETURN NULL;

    -- A single escape character represents an array with a single 
    -- empty element to differentiate from an empty array.
    IF ((SELECT COUNT(0) FROM @original) = 1 AND (SELECT COUNT(0) FROM @original WHERE Element = '') = 1) BEGIN
        RETURN '';
    END

    DECLARE original_cursor CURSOR FOR SELECT Element FROM @original
    OPEN original_cursor  
  
    FETCH NEXT FROM original_cursor INTO @element
  
    WHILE @@FETCH_STATUS = 0  
    BEGIN
        SET @pos = 1
        SET @sb_ = ''
        SET @next = 0

        IF (@element IS NULL) BEGIN
            SET @sb_ = @zed
        END ELSE BEGIN
            WHILE((@pos <= LEN(@element)) AND @next IS NOT NULL) BEGIN
                SET @next = UNICODE(SUBSTRING(@element, @pos, 1));

                IF (NCHAR(@next) IN (@delimiter, @escape) OR (NCHAR(@next) = @zed AND @pos = 1)) BEGIN
                    SET @sb_ = @sb_ + @escape
                END

                SET @sb_ = @sb_ + NCHAR(@next)
                SET @pos = @pos + 1
            END
        END
        
        SET @sb = @sb + @sb_

        FETCH NEXT FROM original_cursor INTO @element

        IF (@@FETCH_STATUS = 0)
            SET @sb = @sb + @delimiter
    END   
    CLOSE original_cursor;  
    DEALLOCATE original_cursor;  

    RETURN @sb
END