Accept null in the issueSetDueDate mutation

app/graphql/mutations/issues/set_due_date.rb

@@ -7,8 +7,17 @@ module Mutations
 
       argument :due_date,
                Types::TimeType,
-               required: true,
-               description: 'The desired due date for the issue.'
+               required: false,
+               description: 'The desired due date for the issue, ' \
+               'due date will be removed if absent or set to null'
+
+      def ready?(**args)
+        unless args.key?(:due_date)
+          raise Gitlab::Graphql::Errors::ArgumentError, 'Argument dueDate must be provided (`null` accepted)'
+        end
+
+        super
+      end
 
       def resolve(project_path:, iid:, due_date:)
         issue = authorized_find!(project_path: project_path, iid: iid)

changelogs/unreleased/accept-null-in-issuesetduedate.yml

+---
+title: Allow issueSetDueDate GraphQL mutation to accept null values
+merge_request: 60139
+author:
+type: added

doc/api/graphql/reference/index.md

@@ -2337,7 +2337,7 @@ Input type: `IssueSetDueDateInput`
 | Name | Type | Description |
 | ---- | ---- | ----------- |
 | <a id="mutationissuesetduedateclientmutationid"></a>`clientMutationId` | [`String`](#string) | A unique identifier for the client performing the mutation. |
-| <a id="mutationissuesetduedateduedate"></a>`dueDate` | [`Time!`](#time) | The desired due date for the issue. |
+| <a id="mutationissuesetduedateduedate"></a>`dueDate` | [`Time`](#time) | The desired due date for the issue, due date will be removed if absent or set to null. |
 | <a id="mutationissuesetduedateiid"></a>`iid` | [`String!`](#string) | The IID of the issue to mutate. |
 | <a id="mutationissuesetduedateprojectpath"></a>`projectPath` | [`ID!`](#id) | The project the issue to mutate is in. |
 

spec/graphql/mutations/issues/set_due_date_spec.rb

@@ -3,8 +3,9 @@
 require 'spec_helper'
 
 RSpec.describe Mutations::Issues::SetDueDate do
-  let(:issue) { create(:issue) }
-  let(:user) { create(:user) }
+  let(:issue) { create(:issue, due_date: '2021-05-01') }
+
+  let_it_be(:user) { create(:user) }
 
   subject(:mutation) { described_class.new(object: nil, context: { current_user: user }, field: nil) }
 
@@ -23,17 +24,25 @@ RSpec.describe Mutations::Issues::SetDueDate do
         issue.project.add_developer(user)
       end
 
-      it 'returns the issue with updated due date' do
+      it 'returns the issue with updated due date', :aggregate_failures do
         expect(mutated_issue).to eq(issue)
         expect(mutated_issue.due_date).to eq(Date.today + 2.days)
         expect(subject[:errors]).to be_empty
       end
 
+      context 'when due date is nil' do
+        let(:due_date) { nil }
+
+        it 'updates due date to be nil' do
+          expect(mutated_issue.due_date).to be nil
+        end
+      end
+
       context 'when passing incorrect due date value' do
         let(:due_date) { 'test' }
 
-        it 'does not update due date' do
-          expect(mutated_issue.due_date).to eq(issue.due_date)
+        it 'updates due date to be nil' do
+          expect(mutated_issue.due_date).to be nil
         end
       end
     end

spec/requests/api/graphql/mutations/issues/set_due_date_spec.rb

@@ -42,12 +42,35 @@ RSpec.describe 'Setting Due Date of an issue' do
     expect(graphql_errors).to include(a_hash_including('message' => error))
   end
 
+  context 'when due date value is a valid date' do
     it 'updates the issue due date' do
       post_graphql_mutation(mutation, current_user: current_user)
 
       expect(response).to have_gitlab_http_status(:success)
       expect(mutation_response['issue']['dueDate']).to eq(2.days.since.to_date.to_s)
     end
+  end
+
+  context 'when due date value is null' do
+    let(:input) { { due_date: nil } }
+
+    it 'updates the issue to remove the due date' do
+      post_graphql_mutation(mutation, current_user: current_user)
+
+      expect(response).to have_gitlab_http_status(:success)
+      expect(mutation_response['issue']['dueDate']).to be nil
+    end
+  end
+
+  context 'when due date argument is not given' do
+    let(:input) { {} }
+
+    it 'returns an error' do
+      post_graphql_mutation(mutation, current_user: current_user)
+
+      expect(graphql_errors).to include(a_hash_including('message' => /Argument dueDate must be provided/))
+    end
+  end
 
   context 'when the due date value is not a valid time' do
     let(:input) { { due_date: 'test' } }