handle the null error if the ElementChemistryDB has null vale in percentage column

OTSIncAMeasureApp/1-OTSMeasure/Measure/DBDataTransition/ElementChemistryDB.cs

@@ -310,7 +310,16 @@ namespace OTSModelSharp.DTLBase
                 nCol = (int)CElementChemistryTable.ColumnID.S_NAME - (int)CElementChemistryTable.ColumnID.MIN;
                 string cheName = Convert.ToString(row[nCol]);
                 nCol = (int)CElementChemistryTable.ColumnID.F_PERCENTAGE - (int)CElementChemistryTable.ColumnID.MIN;
-                double percentage = Convert.ToDouble(row[nCol]);
+
+                double percentage = 0;
+                try
+                {
+                    percentage = Convert.ToDouble(row[nCol]);
+                }
+                catch
+                {
+                    percentage = 0;
+                }
                 CElementChemistryClr che = new CElementChemistryClr(cheName, percentage);
 
                 if (!mapXrayInfo.ContainsKey(fldvec))