When you are asking for empty answers, are you asking for when the students leave an answer blank? If a student does not answer a question, then the exam report will not have any answer in for that question. We do not show 20/5/5 for correct/empty/wrong. If the student does not answer a question, it is marked as wrong as they have not entered the correct answer.
GradeCam is not able to omit one correct answer after four mistakes.