Gridview not updating table when column/cell starts with no data - asp.net

Question

UPDATED: Here is the SP, it doesn't match exactly because of ongoing testing, but you get the jist. Some fields are commented out because of testing....
#tableName Varchar(150),
#new_lang_String nvarchar(max),
-- #lang_String nvarchar(max),
#ID int,
#prev_LangString nvarchar(max) = NULL,
#original_lang_String nvarchar(max) = NULL,
#brief_Descrip nvarchar(max) = NULL,
#submittedBy nvarchar(250) = NULL
AS
/* SET NOCOUNT ON */
DECLARE #lang_String varchar(max);
SET #prev_LangString = #new_lang_String;
DECLARE #submitDate1 DATETIME;
SET #submitDate1 = GETDATE();
DECLARE #sql varchar(max);
SET #lang_String = #original_lang_String;
BEGIN
SET #sql = 'UPDATE ' + #tableName + ' SET [lang_String] = ''' + COALESCE(#lang_String, NULL) + ''', [date_Changed] = ''' + convert(varchar(20), #submitDate1) + ''', [prev_LangString] = ''' + COALESCE(#prev_LangString, NULL) + ''', [brief_Descrip] = ''' + COALESCE(#brief_Descrip, NULL) + ''', [submittedBy] = ''' + #submittedBy + '''
WHERE (ID = ' + CAST(#ID as nvarchar(10)) + '); '
EXECUTE(#sql);
END
RETURN
As you can probably tell in the code I have been struggling with handling the Null in some of the fields as well. Hence the default values inteh update parameters of = " " on some fields.
I am using a gridview to display information that is retrieved from a table in a SQL Express DB. When the user clicks EDIT, and enters information, I am trying to update the table with a STORED PROCEDURE called from the Gridview. See aspx code below.
The issue is that the column which is being edited will not update the DB table unless it had previously had data stored in it, as in the cell in the column IS NOT Null. No errors.
Since most cells in this column are Null to begin with, no data is getting updated. No errors, just nothing written to the table. If the table previously had data within the column cell in question it can be succesfully edited and updated.
Gridview from ASPX Page....
<asp:BoundField DataField="lang_String" HeaderText="Foreign Text" SortExpression="lang_String">
<ControlStyle Width="400px"/>
</asp:BoundField>
Update Command on Gridview calls SP, which works, provided column/cell already had data...
UpdateCommand="EXEC usp_UpdatePTEdit #tableName, #lang_String=#lang_String, #ID=#original_ID, #prev_LangString=#original_lang_String, #brief_Descrip=#brief_Descrip, #submittedBy=#SubmittedBy">
Parameters passed to UpdateCommand, only using a few...
<UpdateParameters>
<asp:SessionParameter Name="tableName" SessionField="tableName1" />
<asp:SessionParameter Name="submittedBy" SessionField="SubmittedByUser" />
<asp:Parameter Name="data_text" Type="String" />
<asp:Parameter Name="lang_String" Type="String" DefaultValue=" " />
<asp:Parameter Name="date_Changed" Type="DateTime" />
<asp:Parameter Name="prev_LangString" Type="String" DefaultValue=" " />
<asp:Parameter Name="needsTranslation" Type="String" />
<asp:Parameter Name="displayRecord" Type="String" />
<asp:Parameter Name="brief_Descrip" Type="String" DefaultValue=" " />
<asp:Parameter Name="original_ID" Type="Int32" />
<asp:Parameter Name="original_data_text" Type="String" />
<asp:Parameter Name="original_lang_String" Type="String" />
<asp:Parameter Name="original_date_Changed" Type="DateTime" />
<asp:Parameter Name="original_prev_LangString" Type="String" />
<asp:Parameter Name="original_needsTranslation" Type="String" />
<asp:Parameter Name="original_displayRecord" Type="String" />
<asp:Parameter Name="original_brief_Descrip" Type="String" />
<asp:Parameter Name="original_submittedBy" Type="String" />
</UpdateParameters>
Everything works if the cell originally has data, "original_lang_String" but if it has not been populated, I can not use the Edit operation of the Gridview to successfully update the table.
Any help or suggestions would be appreciated.

Answer 1

#prev_LangString=#original_lang_String
Depending on what is in usp_UpdatePTEdit, I bet it's failing because somewhere it's checking for an original value that doesn't exist. NULL is special and equality checks for it fail.
Post the code that is in usp_UpdatePTEdit stored proc for more help.

Answer 2

I think the problem may be with the assignment of the parameters to the column of the same name (#lang_String=#lang_String). I recommend specifying the parameters in the order that they appear in the stored proc and remove the #name= syntax. I think that is just going to get the datasource or grid view confused.
Update
I think that you would be better off changing the UpdateCommand to:
UpdateCommand="usp_UpdatePTEdit"
and adding:
UpdateCommandType="StoredProcedure"
This seems to be a better fit for how the update command is designed to work.