title: android firebase database Invalid token in path
body: <p>I did the base64 utf-8 encoding of the email.
  Because it is a database key.
  However, the following problems arise.
  I need help.</p>
  
  <p><strong>setValue at /user/aW1hZ2VfNTk1NkBuYXZlci5jb20=
  failed: DatabaseError: Invalid token in path</strong></p>
  
  <pre><code>databaseReference.child("user").child(util.getBase64encode(email)).setValue(userModel)
  </code></pre>
  
  <p>help me...</p>