Why is javers throwing "argument should not be null" when the compared objects are NOT null, in a mockito test?

I've used javers in a different part of our app. Now I'm adding it to another, and am getting an IllegalArgumentException: argument should not be null. But I have verified (by serializing the objects and logging them) that the 2 objects are NOT null when passed to the compare() method.

Also, this only happens within a unit test run via Mockito. I assume there's a property of the objects that are passed in that is null, and that's what's creating the error. But isn't a null property a valid comparison for javers to detect?

I am using javers version 1.1.

Here's a snippet of my code:

private static final Javers javers = JaversBuilder.javers().build();
Diff difference = javers.compare(object1, object2);

Here's the stack trace:

java.lang.IllegalArgumentException: argument should not be null
    at org.javers.common.validation.Validate.argumentIsNotNull(Validate.java:16)
    at org.javers.common.validation.Validate.argumentIsNotNull(Validate.java:24)
    at org.javers.common.validation.Validate.argumentsAreNotNull(Validate.java:32)
    at org.javers.core.metamodel.type.SetType.map(SetType.java:21)
    at org.javers.core.diff.appenders.SetChangeAppender.calculateEntryChanges(SetChangeAppender.java:63)
    at org.javers.core.diff.appenders.SetChangeAppender.calculateChanges(SetChangeAppender.java:89)
    at org.javers.core.diff.appenders.SetChangeAppender.calculateChanges(SetChangeAppender.java:20)
    at org.javers.core.diff.DiffFactory.appendChanges(DiffFactory.java:142)
    at org.javers.core.diff.DiffFactory.appendPropertyChanges(DiffFactory.java:132)
    at org.javers.core.diff.DiffFactory.createAndAppendChanges(DiffFactory.java:114)
    at org.javers.core.diff.DiffFactory.create(DiffFactory.java:65)
    at org.javers.core.diff.DiffFactory.compare(DiffFactory.java:58)
    at org.javers.core.JaversCore.compare(JaversCore.java:75)

Solution

I updated to version 1.2.1 and that fixed this problem.