Handle null values just in-case

Author: mythz

src/ServiceStack.OrmLite/OrmLiteDialectProviderBase.cs

@@ -712,9 +712,10 @@ public virtual string MergeParamsIntoSql(string sql, IEnumerable<IDbDataParamete
         {
             foreach (var dbParam in dbParams)
             {
-                var varName = dbParam.ParameterName;
-                var quotedValue = GetQuotedValue(dbParam.Value, dbParam.Value.GetType());
-                sql = sql.Replace(varName, quotedValue);
+                var quotedValue = dbParam.Value != null 
+                    ? GetQuotedValue(dbParam.Value, dbParam.Value.GetType())
+                    : "null";
+                sql = sql.Replace(dbParam.ParameterName, quotedValue);
             }
             return sql;
         }