[FIXED JENKINS-9806] the actual fix are in the two previous commits.

changelog.html

@@ -57,6 +57,9 @@ Upcoming changes</a>
 <ul class=image>
   <li class=bug>
   	Validate new view name relative to current context
+  <li class=bug>
+    Unfilled custom workspace textbox shouldn't be allowed.
+    (<a href="http://issues.jenkins-ci.org/browse/JENKINS-9806">issue 9806</a>)
   <li class=rfe>
     "Deploy to Maven repository" post build task should default to unique version, as per Maven3 default.
     (<a href="http://issues.jenkins-ci.org/browse/JENKINS-9807">issue 9807</a>)