title: Can't solve Playground error: Variable \"$input\" of required type \"MemberInput!\" was not provided
body: <p>I've beat on this issue for what seems like a week and nothing online solves it.  No data object is returned, not even "null".  I'm converting from a working REST CRUD app to GraphQL.  Not as easy as I expected.</p>
  
  <p>My mutation in Playground:</p>
  
  <pre><code>mutation createMember($input: MemberInput!) {
      createMember (input: $input) {
            first_name
            last_name
            user_name
      }
  }
  </code></pre>
  
  <p>Playground Query Variables below:  (Not in the headers section.)</p>
  
  <pre><code>{
    "input": {
      "first_name": "John",
      "last_name": "Creston",
      "user_name": "jc"
      }
  }
  </code></pre>
  
  <p>The schema:  (The queries work fine and the Member type, an entity in TypeORM, works with them and full REST CRUD.)</p>
  
  <pre><code>input MemberInput {
      first_name: String!
      last_name: String!
      user_name: String!
  }
  
  type Mutation {
      createMember(input: MemberInput!): Member!
  }
  
  type Query {
      getMembers: [Member]
      getMember(member_id: Int!): Member!
      checkUserName(user_name: String): Member
      checkEmail(email: String): Member
  }
  </code></pre>
  
  <p>I don't see how the resolver could be the problem for this error message but I'll add the Nestjs resolver:</p>
  
  <pre><code>@Mutation('createMember')
    async createMember(@Args('input') input: MemberInput): Promise&lt;Members&gt; {
      console.log('input in resolver: ', input);
      return await this.membersService.addItem(input);
    }
  </code></pre>
  
  <p>The service works with REST and the queries so that should be a problem.  The console.log in the resolver never appears in terminal.</p>
  
  <p>From the Copy CURL button:</p>
  
  <pre><code>curl 'http://localhost:3000/graphql' -H 'Accept-Encoding: gzip,    
  deflate, br' -H 'Content-Type: application/json' -H 'Accept: 
  application/json' -H 'Connection: keep-alive' -H 'DNT: 1' -H 'Origin: 
  http://localhost:3000' --data-binary '{"query":"mutation 
  createMember($input: MemberInput!) {\n  createMember (input: $input) 
  {\n      first_name\n      middle_initial\n      last_name\n     
  user_name\n      pitch\n      main_skill_title\n    \tskill_id_array\n      
  skills_comments\n      other_skills\n      links\n      country\n      
  email\n      member_status\n  }\n}"}' --compressed
  </code></pre>