DGM.println(Object) and friends do a Writer.close() if the object is a writer. Should be flush() instead.

The DefaultGroovyMethods:

print(Object)
println(Object)
print(Object, Object)
println(Object, Object)

all will create a PrintWriter and then do a Writer.close() if self is a Writer. That will close the underlying writer, which is definitely the wrong thing.

The correct behavior is to do a flush().

It is easy to see that flushing rather than closing is the right thing by looking at what happens if self is not a Writer. In that case System.out.print(ln) is called and System.out is not closed.