Set last_step in SchemaCommonFlowHandler (#82616)

* Set last_step in SchemaCommonFlowHandler

* Always use boolean

* Adjust next_step definition

homeassistant/helpers/schema_config_entry_flow.py

@@ -42,8 +42,8 @@ class SchemaFlowFormStep:
     # The next_step function is called if the schema validates successfully or if no
     # schema is defined. The next_step function is passed the union of config entry
     # options and user input from previous steps.
-    # If next_step returns None, the flow is ended with FlowResultType.CREATE_ENTRY.
-    next_step: Callable[[dict[str, Any]], str | None] = lambda _: None
+    # If next_step is None, the flow is ended with FlowResultType.CREATE_ENTRY.
+    next_step: Callable[[dict[str, Any]], str] | None = None
 
     # Optional function to allow amending a form schema.
     # The update_form_schema function is called before async_show_form is called. The
@@ -136,12 +136,11 @@ class SchemaCommonFlowHandler:
         next_step_id: str = step_id
         if user_input is not None or form_step.schema is None:
             # Get next step
-            next_step_id_or_end_flow = form_step.next_step(self._options)
-            if next_step_id_or_end_flow is None:
+            if form_step.next_step is None:
                 # Flow done, create entry or update config entry options
                 return self._handler.async_create_entry(data=self._options)
 
-            next_step_id = next_step_id_or_end_flow
+            next_step_id = form_step.next_step(self._options)
 
         return self._show_next_step(next_step_id)
 
@@ -188,7 +187,10 @@ class SchemaCommonFlowHandler:
 
         # Show form for next step
         return self._handler.async_show_form(
-            step_id=next_step_id, data_schema=data_schema, errors=errors
+            step_id=next_step_id,
+            data_schema=data_schema,
+            errors=errors,
+            last_step=form_step.next_step is None,
         )
 
     async def _async_menu_step(