fix(Editing): set false attribute values on update (openscd#899)

* fix(editing): set false attribute values on update

Since we switched from Replace to Update, we now no longer set falsey
attribute values (like the empty string `''` or `0`). This fixes that
issue.

* test(Editing): add regression test

Co-authored-by: Jakob Vogelsang <[email protected]>

Author: ca-d

src/Editing.ts

@@ -382,7 +382,8 @@ export function Editing<TBase extends LitElementConstructor>(Base: TBase) {
       );
 
       Object.entries(action.newAttributes).forEach(([key, value]) => {
-        if (value) action.element.setAttribute(key, value);
+        if (value !== null && value !== undefined)
+          action.element.setAttribute(key, value);
       });
 
       return true;

test/unit/Editing.test.ts

@@ -341,6 +341,19 @@ describe('EditingElement', () => {
     expect(element).to.not.have.attribute('desc');
   });
 
+  it('allows empty string as attribute value', () => {
+    const newAttributes: Record<string, string | null> = {};
+    newAttributes['name'] = '';
+
+    elm.dispatchEvent(
+      newActionEvent(createUpdateAction(element, newAttributes))
+    );
+
+    expect(element.parentElement).to.equal(parent);
+    expect(element).to.have.attribute('name', '');
+    expect(element).to.not.have.attribute('desc');
+  });
+
   it('does not update an element in case of name conflict', () => {
     const newAttributes: Record<string, string | null> = {};
     newAttributes['name'] = 'Q02';