Guard against NPE, as getGui can return null.
Guard against NPE, as getGui can return null.

git-svn-id: https://svn.apache.org/repos/asf/jmeter/trunk@1783504 13f79535-47bb-0310-9956-ffa450edef68

Former-commit-id: 11ad9bbbbbcb5381f5910ed7f8e7b3ff6a19232a
ham1/jmeter,apache/jmeter,apache/jmeter,etnetera/jmeter,ham1/jmeter,apache/jmeter,etnetera/jmeter,ham1/jmeter,apache/jmeter,benbenw/jmeter,etnetera/jmeter,benbenw/jmeter,etnetera/jmeter,ham1/jmeter,ham1/jmeter,benbenw/jmeter,apache/jmeter,benbenw/jmeter,etnetera/jmeter