Don't build a String when it's not needed

Author: garydgregory

src/main/java/org/apache/commons/lang3/concurrent/ConcurrentUtils.java

@@ -106,7 +106,7 @@ public boolean isDone() {
      * checked exception
      */
     static Throwable checkedException(final Throwable ex) {
-        Validate.isTrue(ExceptionUtils.isChecked(ex), "Not a checked exception: " + ex);
+        Validate.isTrue(ExceptionUtils.isChecked(ex), "Not a checked exception: %s", ex);
         return ex;
     }