Bug 53201 NPE when re-running newly generated javadoc.xml
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javadocexport/JavadocWriter.java
if (p == null)
				continue;
			if (element instanceof ICompilationUnit) {
				String relative= getPathString(p);
				sourcefiles.add(relative);
			} else if (element instanceof IPackageFragment) {
				packages.add(element.getElementName());
			}
		}
	}
	private String getPathString(IPath[] paths) {
		StringBuffer buf= new StringBuffer();
		
		for (int i= 0; i < paths.length; i++) {
			if (buf.length() != 0) {
				buf.append(File.pathSeparatorChar);
			}			
			buf.append(getPathString(paths[i]));
		}
		if (buf.length() == 0) {
			buf.append('.');
		}
		return buf.toString();
	}
	private boolean hasSameDevice(IPath p1, IPath p2) {
		String dev= p1.getDevice();
		if (dev == null) {
			return p2.getDevice() == null;
		}
		return dev.equals(p2.getDevice());