fix issue 36

src/app/utils/formUtils.ts

@@ -79,7 +79,7 @@ export class formUtils {
    */
   public createStructureForm(structure: Structure, isEditMode?: boolean): UntypedFormGroup {
     return new UntypedFormGroup({
-      _id: new UntypedFormControl(structure._id),
+      _id: new UntypedFormControl(structure._id, Validators.required),
       coord: new UntypedFormControl(structure.coord),
       structureType: new UntypedFormControl(structure.structureType, Validators.required),
       structureName: new UntypedFormControl(structure.structureName, Validators.required),