[FIXED JENKINS-16561]

eval("") is no-op in IE but window.execScript("") isn't.
So bring the uniformity outside

changelog.html

@@ -55,6 +55,9 @@ Upcoming changes</a>
 <!-- Record your changes in the trunk here. -->
 <div id="trunk" style="display:none"><!--=TRUNK-BEGIN=-->
 <ul class=image>
+  <li class=bug>
+    Script evaluation script error on IE.
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-16561">issue 16561</a>)
   <li class=bug>
     surefire-reports not detected for android-maven-plugin
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-16776">issue 16776</a>)

war/src/main/webapp/scripts/hudson-behavior.js

@@ -368,6 +368,8 @@ function parseHtml(html) {
  * Evaluates the script in global context.
  */
 function geval(script) {
+    // execScript chokes on "" but eval doesn't, so we need to reject it first.
+    if (script==null || script=="") return;
     // see http://perfectionkills.com/global-eval-what-are-the-options/
     // note that execScript cannot return value
     (this.execScript || eval)(script);
@@ -2143,12 +2145,11 @@ function validateButton(checkUrl,paramList,button) {
           Behaviour.applySubtree(target);
           layoutUpdateCallback.call();
           var s = rsp.getResponseHeader("script");
-          if(s!=null)
-            try {
+          try {
               geval(s);
-            } catch(e) {
+          } catch(e) {
               window.alert("failed to evaluate "+s+"\n"+e.message);
-            }
+          }
       }
   });
 }