Fix crash when showing a cloud plan without a cloud backend

Author: dbanck

internal/cloud/backend.go

@@ -437,7 +437,7 @@ func (b *Cloud) Configure(obj cty.Value) tfdiags.Diagnostics {
 }
 
 func (b *Cloud) AppName() string {
-	if isValidAppName(b.appName) {
+	if b != nil && isValidAppName(b.appName) {
 		return b.appName
 	}
 	return "HCP Terraform"

internal/cloud/backend_test.go

@@ -1705,3 +1705,15 @@ func TestCloud_ServiceDiscoveryAliases(t *testing.T) {
 		t.Fatalf("expected 1 alias but got %d", len(aliases))
 	}
 }
+
+// When a user tries to view a cloud plan without having a cloud backend in their
+// configuration, a call to AppName() would fail with a nil pointer exception
+// See: https://github.com/hashicorp/terraform/issues/37748
+func TestCloud_AppName_with_nil(t *testing.T) {
+	var backend *Cloud = nil
+
+	name := backend.AppName()
+	if name != "HCP Terraform" {
+		t.Fatalf("expected name to be HCP Terraform, got %q", name)
+	}
+}