making it more fool proof. See http://www.nabble.com/plugin-cvstag-tp20312067p20312067.html

git-svn-id: https://hudson.dev.java.net/svn/hudson/trunk/hudson/main@13010 71c3de6d-444a-0410-be80-ed276b4c234a

core/src/main/java/hudson/scm/CVSSCM.java

@@ -991,8 +991,8 @@ public class CVSSCM extends SCM implements Serializable {
         }
 
         public String getCvsExeOrDefault() {
-            if(cvsExe==null)    return "cvs";
-            else                return cvsExe;
+            if(Util.fixEmpty(cvsExe)==null)     return "cvs";
+            else                                return cvsExe;
         }
 
         public void setCvspassFile(String value) {