title: AWS SAM: Unable to unmarshal input
body: <p>I'm trying to build a lambda function with SAM (python3.8).
  I installed the AWS toolkit on VSCode and created the hello_world function.
  SAM Build completed successfully.
  When I run the <em>invoke</em> command with the predefined test/events/event.json I get an exception:</p>
  <pre class="lang-sh prettyprint-override"><code>sam local invoke &quot;TestFunction&quot; -e test/events/event.json
  </code></pre>
  <p>the output:</p>
  <pre class="lang-sh prettyprint-override"><code>{&quot;errorMessage&quot;: &quot;Unable to unmarshal input: Expecting value: line 1 column 1 (char 0)&quot;, &quot;errorType&quot;: &quot;Runtime.UnmarshalError&quot;, &quot;stackTrace&quot;: []}
  </code></pre>
  <p>When running without an event, the function doesn't raise any errors.</p>
  <p>versions:</p>
  <ul>
  <li>SAM CLI, version 1.23.0</li>
  <li>aws-cli/1.18.69 Python/3.8.5 Linux/5.8.0-53-generic botocore/1.16.19</li>
  <li>Docker version 20.10.6, build 370c289</li>
  </ul>
  <p>Can you guide me on how to resolve this problem?</p>