Relax result type validation to avoid nightly build failure

This commit fixes the string result type validation, PR tektoncd#4779 adds
result type and asumes that the default type should be string via
mutating webhook. PR tektoncd#4818 adds the validation for this. However,
resources that did already exist in etcd didn't get the default. So this
commit relaxes the validation for empty result type.

pkg/apis/pipeline/v1beta1/result_types.go

@@ -25,7 +25,7 @@ type TaskResult struct {
 
 	// Description is a human-readable description of the result
 	// +optional
-	Description string `json:"description"`
+	Description string `json:"description,omitempty"`
 }
 
 // TaskRunResult used to describe the results of a task

pkg/apis/pipeline/v1beta1/result_validation.go

@@ -31,6 +31,12 @@ func (tr TaskResult) Validate(ctx context.Context) (errs *apis.FieldError) {
 		return errs.Also(ValidateEnabledAPIFields(ctx, "results type", config.AlphaAPIFields))
 	}
 
+	// Skip the validation for existing resources without specifying a type and not call the setDefaults
+	if tr.Type == "" {
+		return nil
+	}
+
+	// By default the result type is string
 	if tr.Type != ResultsTypeString {
 		return apis.ErrInvalidValue(tr.Type, "type", fmt.Sprintf("type must be string"))
 	}

pkg/apis/pipeline/v1beta1/swagger.json

@@ -2243,8 +2243,7 @@
       "properties": {
         "description": {
           "description": "Description is a human-readable description of the result",
-          "type": "string",
-          "default": ""
+          "type": "string"
         },
         "name": {
           "description": "Name the given name",

pkg/apis/pipeline/v1beta1/task_validation_test.go

@@ -436,6 +436,54 @@ func TestTaskSpecValidate(t *testing.T) {
 	}
 }
 
+func TestTaskSpecResultsValidate(t *testing.T) {
+	type fields struct {
+		Steps   []v1beta1.Step
+		Results []v1beta1.TaskResult
+	}
+	tests := []struct {
+		name   string
+		fields fields
+	}{{
+		name: "valid result type empty",
+		fields: fields{
+			Steps: []v1beta1.Step{{
+				Image: "my-image",
+				Args:  []string{"arg"},
+			}},
+			Results: []v1beta1.TaskResult{{
+				Name:        "MY-RESULT",
+				Description: "my great result",
+			}},
+		},
+	}, {
+		name: "valid result type string",
+		fields: fields{
+			Steps: []v1beta1.Step{{
+				Image: "my-image",
+				Args:  []string{"arg"},
+			}},
+			Results: []v1beta1.TaskResult{{
+				Name:        "MY-RESULT",
+				Type:        "string",
+				Description: "my great result",
+			}},
+		},
+	}}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ts := &v1beta1.TaskSpec{
+				Steps:   tt.fields.Steps,
+				Results: tt.fields.Results,
+			}
+			ctx := getContextBasedOnFeatureFlag("stable")
+			if err := ts.Validate(ctx); err != nil {
+				t.Errorf("TaskSpec.Validate() = %v", err)
+			}
+		})
+	}
+}
+
 func TestTaskSpecValidateError(t *testing.T) {
 	type fields struct {
 		Params       []v1beta1.ParamSpec