I have a form defined in mymodule/src/Form/myForm.php

namespace DrupalmymoduleForm;  use DrupalCoreFormFormBase; use DrupalCoreFormFormStateInterface;  class myForm extends FormBase {  /**  * Specify the form ID.  */ public function getFormId() {   return 'mymodule_myform'; }    /**    * Build the actual form.    */   public function buildForm(array $form, FormStateInterface $form_state) {      // Form API code here... 

Originally, this routing worked fine and the form displayed at the correct path:

mymodule.single_tab:   path: '/node/{node}/edit/performance'   defaults:     _form: 'DrupalmymoduleFormmyForm'     _title: 'Add performance' 

Then I needed to add a custom access check, restricting to a specific content type:

mymodule.single_tab:   path: '/node/{node}/edit/performance'   defaults:     _title: 'Add performance'     _controller: 'DrupalmymoduleControllermymoduleController::content'   requirements:     _custom_access: 'DrupalmymoduleControllermymoduleController::checkAccess' 

The access check works fine. Now I think I have to display my form in the controller:

namespace DrupalmymoduleController;  use DrupalCoreControllerControllerBase; use DrupalCoreFormFormBuilderInterface; use DrupalCoreAccessAccessResult; use DrupalnodeEntityNode;  /**  * Controller for Add Performance single tab.  */ class mymoduleController extends ControllerBase {    /**    * Returns the add single performance form.    */   public function content() {     $form = $this->formBuilder->getForm('DrupalmymoduleFormmyForm');         return [           '#type' => 'markup',           '#markup' => $form         ];   } 

This fails to display the form, and I get:

Call to a member function getForm() on null 

I tried defining my form builder class inside the controller instead, but same result. What am I doing wrong?