Dynamic SQL Query for Custom Paging not returning records

hi i tried one of your sample here is the code below

ALTER PROCEDURE [dbo].[paging](
	@PageNo int = 1,
	@ItemsPerPage int = 20,
	@TotalRows int out,
	@fname varchar(50) = NULL,
	@mname varchar(50) = NULL,
	@lname varchar(50) = NULL,
	@qfr varchar(10) = NULL
	)
AS
BEGIN
  SET NOCOUNT ON
  DECLARE
    @StartIdx int,
    @SQL nvarchar(max),  
    @SQL_Conditions nvarchar(max),  
    @EndIdx int
	
	IF @PageNo < 1 SET @PageNo = 1
	IF @ItemsPerPage < 1 SET @ItemsPerPage = 10

	SET @StartIdx = (@PageNo -1) * @ItemsPerPage + 1
	SET @EndIdx = (@StartIdx + @ItemsPerPage) - 1
	SET @SQL = N'SELECT path_front , pid
                FROM (
                SELECT  ROW_NUMBER() OVER(ORDER BY fname) AS Row, path_front, pid
                      FROM  searcherview 
                      where (fname = @firstname or @firstname = '') and (mname = @midname or @midname = '') and (lname = @lastname or @lastname = '') and (qualifier = @quali or @quali = '')
                       ) AS tbl WHERE  Row >= ' 
						+ CONVERT(varchar(9), @StartIdx) + ' AND
                       Row <=  ' + CONVERT(varchar(9), @EndIdx)
	EXEC sp_executesql @SQL,
	@params = N'@firstname varchar(50), @midname varchar(50), @lastname varchar(50), @quali varchar(10)',
    @firstname = @fname, @midname = @mname, @lastname=@lname, @quali = @qfr
 SET @SQL = 'SELECT @TotalRows=COUNT(*)  FROM searcherview WHERE (fname = @firstname)' 
    EXEC sp_executesql 
        @query = @SQL, 
        @params = N'@TotalRows INT OUTPUT ,@firstname varchar(50)',@firstname = @fname,
        @TotalRows = @TotalRows OUTPUT 
	
END

now when it executes the last sp_executesql returns as expected but the first returs null

is there something wrong with the code specifically in the OR statement?

thanks