The system automatically generates a constructor function for each structured UDT you create. This constructor function returns a UDT value with all attributes initialized to an attribute value of NULL. This does not mean that a field value having the type is itself null. In fact, you can assign a null attributed structured UDT to a column specified with the NOT NULL column attribute.
Externally, the constructor function is a UDF whose name is the same as the structured UDF. You invoke the constructor method with no parameter, for example: udt_name().