Unsupported java.lang.System.lineSeparator() in installer under JRE6

Description of problem:
This error happens to install the installer.jar under JRE6 only.

Stacktrace：
[rzhang@/lab/1brms6/6.0.1/ER1/installer]$rm -rf /tmp/brms-installer && java -jar jboss-brms-installer-6.0.1.GA-redhat-1.jar
Exception in thread "Thread-3" java.lang.NoSuchMethodError: java.lang.System.lineSeparator()Ljava/lang/String;
at com.redhat.installer.util.TruthTable.toString(TruthTable.java:127)
at com.redhat.installer.validator.IsSupportedPlatformValidator.validateData(IsSupportedPlatformValidator.java:51)
at com.izforge.izpack.installer.IzPanel.validatePanel(IzPanel.java:1243)
at com.izforge.izpack.installer.IzPanel.panelValidated(IzPanel.java:435)
at com.izforge.izpack.installer.InstallerFrame.navigateNext(InstallerFrame.java:1664)
at com.izforge.izpack.installer.InstallerFrame.navigateNext(InstallerFrame.java:1649)
at com.izforge.izpack.installer.InstallerFrame$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:662)

Version-Release number of selected component (if applicable):

How reproducible:

Steps to Reproduce:
1.
2.
3.

Actual results:

Expected results:

Additional info: