[Base] Allow useSlotProps to receive undefined elementType

packages/mui-base/src/utils/appendOwnerState.test.ts

@@ -11,6 +11,15 @@ function CustomComponent() {
 }
 
 describe('appendOwnerState', () => {
+  describe('when the provided elementType is undefined', () => {
+    it('returns the provided existingProps without modification ', () => {
+      const existingProps = { className: 'foo' };
+      const actual = appendOwnerState(undefined, existingProps, ownerState);
+
+      expect(actual).to.equal(existingProps);
+    });
+  });
+
   describe('when a DOM element is provided as elementType', () => {
     it('returns the provided existingProps without modification ', () => {
       const existingProps = { className: 'foo' };

packages/mui-base/src/utils/appendOwnerState.ts

@@ -29,7 +29,7 @@ export type AppendOwnerStateReturnType<
 /**
  * Appends the ownerState object to the props, merging with the existing one if necessary.
  *
- * @param elementType Type of the element that owns the `existingProps`. If the element is a DOM node, `ownerState` is not applied.
+ * @param elementType Type of the element that owns the `existingProps`. If the element is a DOM node or undefined, `ownerState` is not applied.
  * @param otherProps Props of the element.
  * @param ownerState
  */
@@ -38,11 +38,11 @@ export default function appendOwnerState<
   OtherProps extends Record<string, any>,
   OwnerState,
 >(
-  elementType: ElementType,
+  elementType: ElementType | undefined,
   otherProps: OtherProps,
   ownerState: OwnerState,
 ): AppendOwnerStateReturnType<ElementType, OtherProps, OwnerState> {
-  if (isHostComponent(elementType)) {
+  if (elementType === undefined || isHostComponent(elementType)) {
     return otherProps as AppendOwnerStateReturnType<ElementType, OtherProps, OwnerState>;
   }
 

packages/mui-base/src/utils/useSlotProps.ts

@@ -22,7 +22,7 @@ export type UseSlotPropsParameters<
   /**
    * The type of the component used in the slot.
    */
-  elementType: ElementType;
+  elementType: ElementType | undefined;
   /**
    * The `slotProps.*` of the unstyled component.
    */