Xcode error due to "There is only one document registered with the given URL."

Question

I can not start Xcode. Whenever it starts, it just crashes with this error:

Application Specific Information:
ProductBuildVersion: 8E3004b
ASSERTION FAILURE in /Library/Caches/com.apple.xbs/Sources/IDEFrameworks/IDEFrameworks-12175.1/IDEKit/Application/IDEDocumentController.m:2136
Details:  There can only be one document registered with a given URL. newDocument:<IDEWorkspaceDocument: 0x7ff6612d6cd0>(  0   -[IDEWorkspaceDocument init] (in IDEKit)
  1   -[NSDocument initForURL:withContentsOfURL:ofType:error:] (in AppKit)
  2   -[IDEWorkspaceDocument initForURL:withContentsOfURL:ofType:error:] (in IDEKit)
  3   -[NSDocumentController makeDocumentForURL:withContentsOfURL:ofType:error:] (in AppKit)
  4   __104-[NSDocumentController makeDocumentForURL:withContentsOfURL:alternateContents:ofType:completionHandler:]_block_invoke (in AppKit)
  5   -[NSDocumentController makeDocumentForURL:withContentsOfURL:alternateContents:ofType:completionHandler:] (in AppKit)
  6   __89-[NSDocumentController reopenDocumentForURL:withContentsOfURL:display:completionHandler:]_block_invoke (in AppKit)

How can I run Xcode again?

EDIT:

Xcode version is 8.3.3

Answer 1

Delete this folder

/Users/<your user name>/Library/Saved\ Application\ State/com.apple.dt.Xcode.savedState

Answer 2

For me, the solution was to remove all custom color pickers in:

~/Library/ColorPickers/