Created attachment 1149099 [details]
logs: engine, proxy, vdsm, chrome

Description of problem:

If a user misses filling out the mandatory fields under Disk Options section: Alias and Size(GB), then clicks "OK" it UI shows:

Uncaught exception occurred. Please try reloading the page. Details: Exception caught: (TypeError) __gwt$exception: <skipped>: Cannot read property 'H' of undefined
Please have your administrator check the UI logs

Version-Release number of selected component:

ovirt-engine-4.0.0-0.0.master.20160310051350.git3151c66.el7.centos.noarch
ovirt-image-common-0.1-1.noarch
vdsm-4.17.999-724.gitb8cb30a.el7.centos.noarch
ovirt-image-daemon-0.1-1.noarch

How reproducible:
100%

Steps to Reproduce:

1. Go to Disks tab.
2. Click on Upload.
3. Choose a file, do not fill in fields: Alias and Size(GB).
4. Click "OK".

Actual results:
UI shows:

Uncaught exception occurred. Please try reloading the page. Details: Exception caught: (TypeError) __gwt$exception: <skipped>: Cannot read property 'H' of undefined
Please have your administrator check the UI logs

From Chrome log:
Wed Apr 20 16:14:05 GMT+300 2016 
SEVERE: Uncaught exception: com.google.gwt.event.shared.UmbrellaException: Exception caught: (TypeError) 
 __gwt$exception: <skipped>: Cannot read property 'H' of undefined
	at Unknown.Ss(webadmin-0.js@24614)
	at Unknown.$s(webadmin-0.js@41)
	at Unknown.F4(webadmin-0.js@19)
	at Unknown.I4(webadmin-0.js@19)
	at Unknown.S3(webadmin-0.js@117)
	at Unknown.Bn(webadmin-0.js@30)
	at Unknown.Ln(webadmin-0.js@23330)
	at Unknown.G_(webadmin-0.js@149)
	at Unknown.Dn(webadmin-0.js@120)
	at Unknown.y3e(webadmin-0.js@699)
	at Unknown.fUe(webadmin-0.js@85)
	at Unknown.hWe(webadmin-0.js@73)
	at Unknown.ev(webadmin-0.js@29)
	at Unknown.iv(webadmin-0.js@57)
	at Unknown.eval(webadmin-0.js@54)
	at Unknown.aA(webadmin-0.js@20)
	at Unknown.c3e(webadmin-0.js@109)
	at Unknown.Qll(webadmin-0.js@2542)
	at Unknown.y3e(webadmin-0.js@317)
	at Unknown.fUe(webadmin-0.js@85)
	at Unknown.eUe(webadmin-0.js@60)
	at Unknown.fWe(webadmin-0.js@58)
	at Unknown.ev(webadmin-0.js@29)
	at Unknown.iv(webadmin-0.js@57)
	at Unknown.eval(webadmin-0.js@54)


Expected results:
1. No exceptions. 
2. Explanation for the users that these are mandatory fields. 

Additional info: