Fix SpotBugs [ERROR] Medium

Switch statement found in
org.apache.commons.logging.impl.SimpleLog.log(int, Object, Throwable)
where default case is missing
[org.apache.commons.logging.impl.SimpleLog] At SimpleLog.java:[lines
505-522] SF_SWITCH_NO_DEFAULT

src/main/java/org/apache/commons/logging/impl/SimpleLog.java

@@ -521,6 +521,10 @@ public class SimpleLog implements Log, Serializable {
         case SimpleLog.LOG_LEVEL_FATAL:
             buf.append("[FATAL] ");
             break;
+        default:
+            // Or throw?
+            buf.append("[UNDEFINED] ");
+            break;
         }
 
         // Append the name of the log instance if so configured