Build successful but simulator screen stays blank & Thread 1: signal SIGABRT

//
//  ViewController.swift
//  AutoLayoutExample5
//
//  Created by patrickmcleod on 2/15/18.
//  Copyright © 2018 Rebel Holdings Corp. All rights reserved.
//

import UIKit

class ViewController: UIViewController {

    let orangeView = UIView()
    let purpleView = UIView()
    let blueView = UIView()

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.

        orangeView.backgroundColor = UIColor(red: 255/255.0, green: 148/255.0, blue: 0/255.0, alpha: 1.0)
        view.addSubview(orangeView)

        purpleView.backgroundColor = UIColor(red: 204/255.0, green: 102/255.0, blue: 255/255.0, alpha: 1.0)
        view.addSubview(purpleView)

        blueView.backgroundColor = UIColor(red: 102/255.0, green: 204/255.0, blue: 255/255.0, alpha: 1.0)
        view.addSubview(blueView)
    }

    override func viewWillLayoutSubviews() {
        setupOrangeViewConstraints()
        setupPurpleViewConstraints()
        setupBlueViewConstraints()
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

   func setupOrangeViewConstraints() {
        orangeView.translatesAutoresizingMaskIntoConstraints = false

        let orangeViewCenterXConstraint = NSLayoutConstraint(item: orangeView, attribute: .centerX, relatedBy: .equal, toItem: view, attribute: .centerX, multiplier: 1.0, constant: 0.0)
        let orangeViewBottomConstraint = NSLayoutConstraint(item: orangeView, attribute: .bottom, relatedBy: .equal, toItem: view, attribute: .bottomMargin, multiplier: 1.0, constant: -50.0)
        let orangeViewHeightXConstraint = NSLayoutConstraint(item: orangeView, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1.0, constant: 57.0)
        let orangeViewWidthConstraint = NSLayoutConstraint(item: orangeView, attribute: .width, relatedBy: .equal, toItem: view, attribute: .notAnAttribute, multiplier: 1.0, constant: 200.0)

        view.addConstraints([
            orangeViewWidthConstraint, orangeViewBottomConstraint, orangeViewCenterXConstraint, orangeViewHeightXConstraint])
    }

    func setupPurpleViewConstraints() {
        purpleView.translatesAutoresizingMaskIntoConstraints = false

        let purpleViewLeadingSpaceConstraint = NSLayoutConstraint(item: purpleView, attribute: .leading, relatedBy: .equal, toItem: view, attribute: .leadingMargin, multiplier: 1.0, constant: 8.0)
        let purpleViewBottomSpaceConstraint = NSLayoutConstraint(item: purpleView, attribute: .bottom, relatedBy: .equal, toItem: orangeView, attribute: .topMargin, multiplier: 1.0, constant: -8.0)
        let purpleViewTrailingSpaceConstraint = NSLayoutConstraint(item: purpleView, attribute: .trailing, relatedBy: .equal, toItem: blueView, attribute: .leadingMargin, multiplier: 1.0, constant: -8.0)
        let purpleViewTopSpaceConstraint = NSLayoutConstraint(item: purpleView, attribute: .top, relatedBy: .equal, toItem: view, attribute: .topMargin, multiplier: 1.0, constant: 8.0)

        view.addConstraints([
            purpleViewTopSpaceConstraint, purpleViewBottomSpaceConstraint, purpleViewLeadingSpaceConstraint, purpleViewTrailingSpaceConstraint])
    }

   func setupBlueViewConstraints() {
        blueView.translatesAutoresizingMaskIntoConstraints = false

        let blueViewTopSpaceConstraint = NSLayoutConstraint(item: blueView, attribute: .top, relatedBy: .equal, toItem: view, attribute: .topMargin, multiplier: 1.0, constant: 8.0)
        let blueViewBottomSpaceConstraint = NSLayoutConstraint(item: blueView, attribute: .bottom, relatedBy: .equal, toItem: orangeView, attribute: .topMargin, multiplier: 1.0, constant: -8.0)
        let blueViewTrailingSpaceConstraint = NSLayoutConstraint(item: blueView, attribute: .trailing, relatedBy: .equal, toItem: view, attribute: .trailingMargin, multiplier: 1.0, constant: -8.0)
        let equalWidthConstraint = NSLayoutConstraint(item: blueView, attribute: .width, relatedBy: .equal, toItem: purpleView, attribute: .width, multiplier: 1.0, constant: 0.0)

        view.addConstraints([
            blueViewTopSpaceConstraint, blueViewBottomSpaceConstraint, blueViewTrailingSpaceConstraint, equalWidthConstraint])
    }

}