title: Why do I get an error when upgrading from ExtJS 4.2.1 to ExtJS 5?
body: <p>I executed the following as specified in the ExtJS 5 upgrade guide:</p>
  
  <p>sencha app upgrade -ext</p>
  
  <p>And I got this output with error:</p>
  
  <pre><code>sencha app upgrade -ext
  Sencha Cmd v5.0.0.160
  [INF] Downloading ext package...
  [INF] Source File : http://cdn.sencha.com/cmd/packages/e....0.970/ext.pkg
  [INF] Downloading : ....................
  [INF] Extracting ext package...
  [INF] Package is already local: ext/5.0.0.970
  [INF] Extracting : ....................
  [INF] Loading configuration for framework directory: C:\Sencha\Cmd\repo\extract\ext\5.0.0.970
  [INF] Removing existing framework at C:\atlantis\amc\gui\src\main\ext
  [INF] upgrading application
  [INF] Upgrading to sdk at C:\atlantis\amc\gui\src\main\ext
  [INF] Updating application and workspace from Ext JS 4.2.1.883 / Cmd 4.0.2.67
  [WRN] Use merge tool to resolve conflict: C:\atlantis\amc\gui\src\main\usx\.sencha\app\sencha.cfg
  [ERR]
  [ERR] BUILD FAILED
  [ERR] com.sencha.exceptions.ExProcess: Failed creating background process
  [ERR]
  [ERR] Total time: 1 second
  [ERR] org.mozilla.javascript.WrappedException: Wrapped com.sencha.exceptions.BasicException: com.sencha.exceptions.ExProcess: Failed creating background process
  (C:\Sencha\Cmd\5.0.0.160\ant\ant-util.js#849)
  [ERR]
  The application was last modified by an older version of Sencha Cmd (4.0.2.67)
  the current is 5.0.0.160.
  Please run "sencha app upgrade" to update to 5.0.0.160.
  </code></pre>
  
  <p>And when I execute simply "sencha app upgrade" I get this:</p>
  
  <pre><code>Sencha Cmd v5.0.0.160
  [INF] upgrading application
  [INF] Upgrading to sdk at C:\atlantis\amc\gui\src\main\ext
  [INF] Updating application and workspace from Ext JS 4.2.1.883 / Cmd 3.0.0.250
  [ERR] org.mozilla.javascript.WrappedException: Wrapped java.lang.NullPointerException (anonymous#336)
  [ERR]
  The application was last modified by an older version of Sencha Cmd (0.0.0.0)
  the current is 5.0.0.160.
  Please run "sencha app upgrade" to update to 5.0.0.160. 
  </code></pre>