improved sql parser.

src/main/java/com/alibaba/druid/util/StringUtils.java

@@ -122,6 +122,10 @@ public class StringUtils {
         return a.equalsIgnoreCase(b);
     }
 
+    public static boolean isEmpty(String value) {
+        return isEmpty((CharSequence) value);
+    }
+
     public static boolean isEmpty(CharSequence value) {
         if (value == null || value.length() == 0) {
             return true;