GetBrowserClassString() Throws Error when installing a package in SXP8.1U3

Question

Having problems when uploading a Sitecore Package from one environment to the next. Both environments have the same version level (Sitecore XP 8.1U3 / EXM 3.3).

Screen error message reads:

[NullReferenceException: Object reference not set to an instance of an object.]
   Sitecore.UIUtil.GetBrowserClassString() +347
   Sitecore.Shell.Controls.Standard.FormPageXmlControl.OnLoad(EventArgs e) +1154
   System.Web.UI.Control.LoadRecursive() +67
   System.Web.UI.Control.LoadRecursive() +164
   System.Web.UI.Control.LoadRecursive() +164
   System.Web.UI.Control.LoadRecursive() +164
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +4497

Sitecore Log Output:

3028 15:10:20 INFO  File has been uploaded: D:\inetpub\wwwroot\Sitecore\Data\packages\ClientMailCoreSpeakApplication.zip
ManagedPoolThread #5 15:10:25 INFO  Job started: Install
ManagedPoolThread #5 15:10:25 INFO  Installing package: D:\inetpub\wwwroot\Sitecore\Data\packages\ClientMailCoreSpeakApplication.zip
ManagedPoolThread #5 15:10:56 INFO  Installation was aborted at entry: items/core/sitecore/client/Applications/Client Mail/{B1F6C86A-4F1D-4A60-8949-EC945ABE0675}/en/1/xml
ManagedPoolThread #5 15:10:56 INFO  Installation was aborted
ManagedPoolThread #5 15:10:56 INFO  Job ended: Install (units processed: )

Note that the Sitecore log does NOT show the 500 error displayed to the browser.

Process:

1. Upload Package File - Successful.
2. Click through to Name and License Dialog - Successful.
3. Clicking the Install button immediately throws an error.

Package Contains:

Contains Sitecore items meant for the core database to install a new Speak Application.

Answer 1

Given this works for you on other environments with (presumably) the same code, the problem is most likely somewhere in the databases or files not in version control (including tokenized files).

Whenever I see a NullReferenceException without any obvious clue as to what was null, I go straight to the source code.

Sitecore.UIUtil.GetBrowserClassString(), the method throwing the null-ref exception, has the following source code:

public static string GetBrowserClassString()
{
  string str = string.Empty;
  if (UIUtil.IsIE())
    str = str + " ie" + " ie" + (object) UIUtil.GetBrowserMajorVersion();
  else if (UIUtil.IsFirefox())
    str = str + " ff" + " ff" + (object) Client.Device.Capabilities.Browser.MajorVersion;
  else if (UIUtil.IsWebkit())
    str = str + " ff" + " wk" + " wk" + (object) Client.Device.Capabilities.Browser.MajorVersion;
  return str.Trim();
}

The most likely part of that code that could reasonably be null (thanks to statics and value types) is Client.Device. Perhaps you have some site in <sites> misconfigured, or one of the devices in /sitecore/layout/devices is missing or misconfigured (for example, the Capabilities object might be null if your Sitecore instance has something odd in the Capabilities Type field).