When assessing student work, graders will often find that some students will leave one or more problems blank on assessments. Since there is no work shown, the grader has no means to evaluate the student's understanding of a particular problem, and thus awards zero points. This practice punishes the student behavior of leaving a problem blank, but this zero is not necessarily an accurate assessment of student understanding of a particular topic. While some might argue that this grading practice is "fair" in that students know that they can't receive points for answers they don't submit, we share evidence that different student groups engage in blank-leaving behavior at different rates and are therefore unequally impacted. We analyze 10 years of UC Davis introductory physics course databases to show that different groups of students skip problems and entire exams at different rates. We also share some implications for grading practices.