This would suggest that outputStream is null, which usually means it was never initialized in the first place.
You seem to have two constructors that does two different things. One that initializes outputStream and one that does not. Every constructor should initialize every member variable. Multiple constructors are usually set up so that one takes the most possible parameters and the others takes less by explicitly calling the first constructor with hard-coded default values.
You cannot divide initialization over several constructors. If you feel that the parameter list would be too long to initialize all variables you can wrap related parameters in other classes or containers