Description of problem:
 Setting "" string to any of Infinispan Configuration screen input fields ends with NPE and stucked installer.

Version-Release number of selected component (if applicable):
 EAP 6.2.0.ER5

How reproducible:
 always

Steps to Reproduce:
 1. Run gui installer, use default options until Post-install Configuration screen.
 2. Set to Perform additional post-install configuration and select to Install Infinispan Cache
 3. Put "" to Infinispan Name input field and click on Next button.

Actual results:
Exception in thread "Thread-39" java.lang.NullPointerException
	at com.izforge.izpack.panels.UserInputPanel.readTextField(UserInputPanel.java:2145)
	at com.izforge.izpack.panels.UserInputPanel.readInput(UserInputPanel.java:1370)
	at com.izforge.izpack.panels.UserInputPanel.isValidated(UserInputPanel.java:1231)
	at com.izforge.izpack.installer.IzPanel.panelValidated(IzPanel.java:434)
	at com.izforge.izpack.installer.InstallerFrame.navigateNext(InstallerFrame.java:1664)
	at com.izforge.izpack.installer.InstallerFrame.navigateNext(InstallerFrame.java:1649)
	at com.izforge.izpack.installer.InstallerFrame$NavigationHandler.navigate(InstallerFrame.java:1812)
	at com.izforge.izpack.installer.InstallerFrame$NavigationHandler.access$100(InstallerFrame.java:1779)
	at com.izforge.izpack.installer.InstallerFrame$NavigationHandler$1.run(InstallerFrame.java:1796)
	at java.lang.Thread.run(Thread.java:724)
and installer will freeze.

Expected results:
 Error dialog is thrown.