We experimented to find Null Pointer Exception bugs in 51 popular libraries, and reported 21 bugs to the maintainers of each library. Of these, 15 reports have been patched, 4 reports are still open, and 2 reports were rejected. The table below lists the reported bugs. Project Report Status Activiti Issue 4553 Open Apache Commons BCEL Issue 289 Open Apache Commons Configuration Issue 355 Patched Apache Commons Configuration Issue 365 Patched Apache Commons Configuration Issue 368 Patched Apache Commons Configuration Issue 381 Patched Apache Commons Configuration Issue 382 Rejected Apache Commons DBCP Issue 352 Patched Apache Commons IO Issue 569 Rejected Apache Commons Math Issue 236 Open Apache Johnzon Issue 117 Patched Apache Johnzon Issue 123 Patched Apache Karaf Issue 1825 Patched Apache Karaf Issue 1826 Patched Apache PDFBox Issue 178 Patched Apache TsFile Issue 50 Open Feign Issue 2304 Patched JSqlParser Issue 1965 Patched Kubernetes Java Client Issue 3081 Patched Nutz Issue 1613 Open OpenGrok Issue 4542 Patched