fix(form-core): allow popultion conditionally rendered fields

.changeset/big-bags-provide.md

@@ -0,0 +1,10 @@
+---
+'@lion/fieldset': patch
+'@lion/form-core': patch
+---
+
+Field population fix
+
+#### Bugfixes
+
+- allow population conditionally rendered fields in formGroup/fieldset/form

packages/fieldset/test/lion-fieldset.test.js

@@ -342,6 +342,33 @@ describe('<lion-fieldset>', () => {
     expect(el.modelValue).to.eql({ lastName: 'Bar' });
   });
 
+  it('does not fail when conditional (not rendered) formElements are populated', async () => {
+    const showC = false;
+    const el = await fixture(html`
+      <${tag}>
+        <label slot="label">My Label</label>
+        <${childTag} name="a"></${childTag}>
+        <${childTag} name="b"></${childTag}>
+        ${showC ? html`<${childTag} name="c"></${childTag}>` : ''}
+      </${tag}>
+    `);
+    expect(el.formElements.a).to.be.not.undefined;
+    expect(el.formElements.b).to.be.not.undefined;
+    expect(el.formElements.c).to.be.undefined;
+
+    let wasSuccessful = false;
+    try {
+      // c does not exist, because it is not render
+      el.serializedValue = { a: 'x', b: 'y', c: 'z' };
+      wasSuccessful = true;
+      // eslint-disable-next-line no-empty
+    } catch (_) {}
+
+    expect(wasSuccessful).to.be.true;
+    expect(el.formElements.a.serializedValue).to.equal('x');
+    expect(el.formElements.b.serializedValue).to.equal('y');
+  });
+
   describe('Validation', () => {
     it('validates on init', async () => {
       class IsCat extends Validator {

packages/form-core/src/form-group/FormGroupMixin.js

@@ -332,7 +332,9 @@ export const FormGroupMixin = dedupeMixin(
                 el[property] = values[name][index]; // eslint-disable-line no-param-reassign
               });
             }
-            this.formElements[name][property] = values[name];
+            if (this.formElements[name]) {
+              this.formElements[name][property] = values[name];
+            }
           });
         }
       }