java.lang.nullpointerexception

java.lang.NullPointerException is a runtime error that occurs when a program attempts to use an object reference that has a null value. In other words, the program is trying to access or manipulate an object that does not exist or has not been initialized. This can happen when a variable or object is not properly initialized, or when it is set to null intentionally or accidentally. To fix this error, the program needs to ensure that all object references are properly initialized before they are used.