title: Warning: Encountered two children with the same key, `-`. Keys should be unique so that components maintain their identity across updates
body: <p>I am running a code snippet as follow:</p>
  
  <pre><code>renderPropositions() {
          const items = this.props.propositionAddress.map(async address =&gt; {
              // get the instance of deployed contract
              const instance = new web3.eth.Contract(JSON.parse(Proposition.interface), address);
  
              const title = await instance.methods.pTitle().call();
  
              return {
                  header: title,
                  meta: address
              }
          });
  
          return &lt;Card.Group items={items} /&gt;;
  
      }
  </code></pre>
  
  <p>This continually hit the error above. But when I drop the <code>async</code> and <code>await</code> functions, there is no error.</p>
  
  <p>Could anyone help?</p>