Only display add button if at least one entity is selected in entities picker (#27699)

src/components/entity/ha-entities-picker.ts

@@ -147,7 +147,7 @@ class HaEntitiesPicker extends LitElement {
           .createDomains=${this.createDomains}
           .required=${this.required && !currentEntities.length}
           @value-changed=${this._addEntity}
-          add-button
+          .addButton=${currentEntities.length > 0}
         ></ha-entity-picker>
       </div>
     `;

src/components/ha-form/ha-form.ts

@@ -148,7 +148,7 @@ export class HaForm extends LitElement implements HaFormElement {
                   .value=${getValue(this.data, item)}
                   .label=${this._computeLabel(item, this.data)}
                   .disabled=${item.disabled || this.disabled || false}
-                  .placeholder=${item.required ? "" : item.default}
+                  .placeholder=${item.required ? undefined : item.default}
                   .helper=${this._computeHelper(item)}
                   .localizeValue=${this.localizeValue}
                   .required=${item.required || false}