title: Map() function returning as undefined when attempting to return query
body: <p>I'm having issues returning data from a simple query. I properly executed this with Apollo's test application (<a href="https://codesandbox.io/s/nn9y2wzyw4" rel="nofollow noreferrer">https://codesandbox.io/s/nn9y2wzyw4</a>), but when I attempt it with data from my local server it is throwing me a TypeError: Cannot read property 'map' of undefined. The query is showing up in my console log and on the GraphQL playground.</p>
  
  <p>The only way to return data I have found so far is the map function, but I realize it may not be applicable in this situation. I have tried formatting my return statement a million ways but do not seem to get it. I understand it is likely a very simple solution.</p>
  
  <pre><code>import React from "react";
  import { render } from "react-dom";
  
  import ApolloClient from "apollo-boost";
  import { ApolloProvider, useQuery } from "@apollo/react-hooks";
  import gql from "graphql-tag";
  
  const client = new ApolloClient({
    uri: "http://localhost:4000/graphql"
  });
  
  function GetPokemon() {
    const { loading, error, data } = useQuery(gql`
      {
        pokemonById(id: "003") {
          id
          name
        }
      }
    `);
  
    if (loading) return &lt;p&gt;Loading...&lt;/p&gt;;
    if (error) return &lt;p&gt;Error :(&lt;/p&gt;;
  
    console.log(data);
  
    return data.pokemonById.map((id, name) =&gt; (
      &lt;div key={id}&gt;
        &lt;p&gt;
          {id}: {name}
        &lt;/p&gt;
      &lt;/div&gt;
    ));
  }
  
  export const App = () =&gt; (
    &lt;ApolloProvider client={client}&gt;
      &lt;div&gt;
        &lt;h2&gt;My first Apollo app &lt;/h2&gt;
        &lt;GetPokemon /&gt;
      &lt;/div&gt;
    &lt;/ApolloProvider&gt;
  );
  </code></pre>
  
  <p>For more context, I am using a local version of this GraphQL server: <a href="https://github.com/axelhzf/graphql-pokemon-server" rel="nofollow noreferrer">https://github.com/axelhzf/graphql-pokemon-server</a></p>
  
  <p>And in the playground, my query appears as the following:</p>
  
  <pre><code>{
    "data": {
      "pokemonById": {
        "id": "003",
        "name": "Venusaur"
      }
    }
  }
  </code></pre>