What is the purpose of creating an empty constructor in a POJO class?

public Employee(){}

In java if you don't declare a Const. Then it makes its own which is called as default Const. However now I days frameworks makes it mandatory to declare a no argument construct with a parameterized Constr.

Therefore
First it is used to override default construct and meet pojo specification
Second it used to provide default values like null and - 1