Fix NPE when applying "String.isBlank() rather than
String.strip().isEmpty()" cleanup to the following code:

void foo(String s) {
	if (equals(s.strip())) {
		System.out.println("bug 573831");
	}
}

Change-Id: I047870cdf4995e621b7aed926714d26116eef160
Signed-off-by: Holger Voormann <eclipse@voormann.de>
Reviewed-on: https://git.eclipse.org/r/c/jdt/eclipse.jdt.ui/+/181134
Tested-by: JDT Bot <jdt-bot@eclipse.org>
Reviewed-by: Fabrice Tiercelin <fabrice.tiercelin@yahoo.fr>