[FIXED JENKINS-3539] Prevent empty file creation if left empty
Merge branch 'master' of https://github.com/jenkinsci/jenkins into JENKINS-3539

Conflicts:
	test/src/test/java/hudson/model/ParametersTest.java
Merge pull request #1428 from daniel-beck/JENKINS-3539

[FIXED JENKINS-3539] Prevent empty file creation if left empty