If you pass the following piece code through javac
public class Test {
;
{

a block tree node is generated by javac for the semi-colon inside the class Test. The fields pos and endpos of tree node are set to -1. Trying to generate the source code based on the tree results in the following code
public class Test {
{
}
{

This affects the tools depending on javac for source modelling. See a related bug 6357517 which is filed against Java Studio Creator