Update StringUtils.java

changing str.length() == 0 to str.isEmpty()

Author: fyf4067

src/main/java/com/mastercard/developer/utils/StringUtils.java

@@ -6,6 +6,6 @@ private StringUtils() {
     }
 
     public static boolean isNullOrEmpty(String str) {
-        return null == str || str.length() == 0;
+        return null == str || str.isEmpty();
     }
-}
+}