SQL Toolkit - The field/column contains null

Hello, 

I'm getting an error when trying to read an empty field in my database.

The problem apprear when reading the filed 9 and 10. But not with the fields 5 and 6. I copied the columns 5 and 6 to create columns 9 and 10. I changed the title of these columns of course. 

All fields of these column are empty when executing my code. I should get an empty string as field 5 and 6, but when arriving to the filed 9 :

DBGetColChar (iHstmt, 9, &tcCode, "");   //Column 9

I get this error message : 

NON-FATAL RUN-TIME ERROR:   "DB.c", line 2655, col 9, thread id 0x00001F40:   Function DBGetColChar: (return value == -2 [0xfffffffe]). The field/column contains null.

Here is my code : 

....
iHstmt = DBActivateSQL (tiConnectionHandle[iConnectionBase], tcMessage);   
l_NumberOfRecords = DBNumberOfRecords(iHstmt);
   for(int recLoop = 0; recLoop < l_NumberOfRecords; recLoop++)
   {
	    if( DBFetchNext (iHstmt) != DB_SUCCESS) break;
..............
// Get field 5
DBGetColChar (iHstmt, 5, &tcCode, "");  //Column 5
		l_s_Alias.name =  (char*) malloc(strlen(tcCode)+1);
		strcpy(l_s_Alias.name,tcCode);
		DBFree(tcCode);
// Get field 6
DBGetColChar (iHstmt, 6, &tcCode, "");  //Column 6
		l_s_Alias.name =  (char*) malloc(strlen(tcCode)+1);
		strcpy(l_s_Alias.name,tcCode);
		DBFree(tcCode);
// Get field 9
DBGetColChar (iHstmt, 9, &tcCode, "");   //Column 9
		l_s_Alias.name =  (char*) malloc(strlen(tcCode)+1);
		strcpy(l_s_Alias.name,tcCode);
		DBFree(tcCode);
// Get field 10
DBGetColChar (iHstmt, 10, &tcCode, "");   //Column 10
		l_s_Alias.name =  (char*) malloc(strlen(tcCode)+1);
		strcpy(l_s_Alias.name,tcCode);
		DBFree(tcCode);
   }
    DBDeactivateSQL(iHstmt);

...

I checked the Default value of all fields in my Access DB, it's an empty string : ""

Any idea to solve this problem please ? 

Regards,

Blue