fix: resolve panic issue in pipeline controller caused by CustomRun

fix #8561

When validating the optional workspace of the pipeline, encountering a CustomRun
should not cause a panic, as this configuration will be validated again during
the creation of the CustomRun.

pkg/reconciler/pipelinerun/resources/validate_dependencies.go

@@ -101,12 +101,10 @@ func ValidateOptionalWorkspaces(pipelineWorkspaces []v1.PipelineWorkspaceDeclara
 
 	for _, rpt := range state {
 		for _, pws := range rpt.PipelineTask.Workspaces {
-			if optionalWorkspaces.Has(pws.Workspace) {
+			if rpt.ResolvedTask != nil && rpt.ResolvedTask.TaskSpec != nil && optionalWorkspaces.Has(pws.Workspace) {
 				for _, tws := range rpt.ResolvedTask.TaskSpec.Workspaces {
-					if tws.Name == pws.Name {
-						if !tws.Optional {
-							return fmt.Errorf("pipeline workspace %q is marked optional but pipeline task %q requires it be provided", pws.Workspace, rpt.PipelineTask.Name)
-						}
+					if tws.Name == pws.Name && !tws.Optional {
+						return fmt.Errorf("pipeline workspace %q is marked optional but pipeline task %q requires it be provided", pws.Workspace, rpt.PipelineTask.Name)
 					}
 				}
 			}

pkg/reconciler/pipelinerun/resources/validate_dependencies_test.go

@@ -422,6 +422,23 @@ func TestValidateOptionalWorkspaces_ValidStates(t *testing.T) {
 				},
 			},
 		}},
+	}, {
+		desc: "pipeline with optional workspace combined with customrun",
+		workspaces: []v1.PipelineWorkspaceDeclaration{{
+			Name:     "ws1",
+			Optional: true,
+		}},
+		state: prresources.PipelineRunState{{
+			PipelineTask: &v1.PipelineTask{
+				Name: "pt1",
+				Workspaces: []v1.WorkspacePipelineTaskBinding{{
+					Name:      "foo",
+					Workspace: "ws1",
+				}},
+			},
+			ResolvedTask: nil,
+			CustomTask:   true,
+		}},
 	}} {
 		t.Run(tc.desc, func(t *testing.T) {
 			if err := prresources.ValidateOptionalWorkspaces(tc.workspaces, tc.state); err != nil {