Replace Arrays#asList with Collections.singletonList

[wikumChamith]

This fixes the com.thoughtworks.xstream.converters.ConversionException: No converter available error when running the 2.x snapshot.

Related ticket: https://openmrs.atlassian.net/browse/SXS-37

[dkayiwa]

Did you create a ticket for this?

[wikumChamith]

Did you create a ticket for this?

I couldn't find the JIRA project for this. I am planning to link this with: https://openmrs.atlassian.net/browse/SXS-37

[dkayiwa]

On the ticket, fully describe the details that led to this pull request.

[wikumChamith]

On the ticket, fully describe the details that led to this pull request.

I added a comment to ticket: https://openmrs.atlassian.net/browse/SXS-37?focusedCommentId=148941

[dkayiwa]

Do you mind also explaining a bit what used to cause this problem and how the singleton fixes it?

[wikumChamith]

Do you mind also explaining a bit what used to cause this problem and how the singleton fixes it?

Arrays.asList() returns an instance of java.util.Arrays$ArrayList which is different from java.util.ArrayList. java.util.Arrays$ArrayList is a private inner class. So when XStream tries to use reflection to serialize fields like modCount, it gets blocked.

private static class ArrayList<E> extends AbstractList<E> implements RandomAccess, Serializable {

Collections.singletonList() returns an instance of: java.util.Collections$SingletonList. This is also a private class, but it doesn't override or expose problematic fields like modCount.