Insert '@NotNull' on parameter 'a'

`@NotNull` is an annotation used in Java to indicate that a parameter, field, or method return value cannot be null. To add `@NotNull` annotation on parameter 'a', you can modify the method signature as follows:

public void myMethod(@NotNull Object a) {
   // method implementation
}

Note that you will need to import the `@NotNull` annotation from the appropriate library, depending on the framework or tool you are using.