BeanCopier.copy throws a NullPointerException if the target bean contains a property without a setter and the copier tries to set that property. It should skip read-only properties. The cause is that BeanCopier.generateClass reads the property getters instead the setters of the target bean. I've attached a patch which adds a testcase demonstrating the error and a fix for the BeanCopier.
This bug is the same as bugs 1516879 and 1516861. I have opened a new bug because I wanted to provide a better summary and add the patch.