title: ArangoDB Exceptions
body: <p>I was running commands in the tutorial, and I noticed that I kept getting exceptions that didn't seem like part of the normal operation of the shell.  </p>
  
  <p>Command</p>
  
  <pre><code>arangosh [_system]&gt; db._update(doc, { someValue: 42 });
  </code></pre>
  
  <p>Output</p>
  
  <pre><code>JavaScript exception in file 'c:/Program Files/ArangoDB 2.5.4/share/arangodb/js/
  client/modules/org/arangodb/arango-database.js' at 789,11: [ArangoError 1200: pr
  econdition failed]
  
  !    throw new ArangoError(requestResult);
  !          ^
  stacktrace: Error
      at ArangoDatabase._update (c:/Program Files/ArangoDB 2.5.4/share/arangodb/js
  /client/modules/org/arangodb/arango-database.js:789:11)
  
      at &lt;shell command&gt;:1:4
  </code></pre>