Проверьте, пустая ли строка Java
if (myString == null || myString.equals(""))
throw new IllegalArgumentException("empty string");
ExceptionThrower
if (myString == null || myString.equals(""))
throw new IllegalArgumentException("empty string");if(str != null && !str.isEmpty())
Be sure to use the parts of && in this order, because java will not proceed to evaluate the second part if the first part of && fails, thus ensuring you will not get a null pointer exception from str.isEmpty() if str is null.