Changing the StringBuilder to build around an empty String and not null, as null will cause an NPE. Reported by FindBugs

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/lang/trunk@1006333 13f79535-47bb-0310-9956-ffa450edef68

src/main/java/org/apache/commons/lang3/AnnotationUtils.java

@@ -59,7 +59,7 @@ public class AnnotationUtils {
                     break;
                 }
             }
-            return new StringBuilder(annotationType == null ? null : annotationType.getName())
+            return new StringBuilder(annotationType == null ? "" : annotationType.getName())
                     .insert(0, '@').toString();
         }