[Simple-support] NullPointerException when attempting to serialize multiply nested generic maps

[Stanislaw O. <sta...@ca...>]

Hello,

I thought I'd let you know that an attempt to serialize an object of class
like this:

    @Root
    private static class ToSerialize
    {
        @ElementMap
        public Map<String, Map<String, String>> map;
    }

results (v2.0.2) in a NullPointerException:

Exception in thread "main" java.lang.NullPointerException
    at org.simpleframework.xml.core.Support.isPrimitive(Support.java:268)
    at org.simpleframework.xml.core.Source.isPrimitive(Source.java:167)
    at org.simpleframework.xml.core.Entry.getValue(Entry.java:191)
    at
org.simpleframework.xml.core.CompositeMap.<init>(CompositeMap.java:96)
    at
org.simpleframework.xml.core.ElementMapLabel.getConverter(ElementMapLabel.java:121)
    at
org.simpleframework.xml.core.CacheLabel.getConverter(CacheLabel.java:162)
    at
org.simpleframework.xml.core.Composite.writeElement(Composite.java:986)
    at
org.simpleframework.xml.core.Composite.writeElements(Composite.java:881)
    at org.simpleframework.xml.core.Composite.write(Composite.java:787)
    at org.simpleframework.xml.core.Composite.write(Composite.java:763)
    at org.simpleframework.xml.core.Traverser.write(Traverser.java:217)
    at org.simpleframework.xml.core.Traverser.write(Traverser.java:190)
    at org.simpleframework.xml.core.Traverser.write(Traverser.java:168)
    at org.simpleframework.xml.core.Persister.write(Persister.java:921)
    at org.simpleframework.xml.core.Persister.write(Persister.java:903)
    at org.simpleframework.xml.core.Persister.write(Persister.java:884)
    at org.simpleframework.xml.core.Persister.write(Persister.java:1000)
    at org.simpleframework.xml.core.Persister.write(Persister.java:982)
    at org.simpleframework.xml.core.Persister.write(Persister.java:963)

I'm not sure -- is this a bug or some design decision/limitation related to
generics? I'm asking more out of curiosity because I'm happy with a
workaround based on creating a wrapper class that contains a field
corresponding to the "inner" map of the problematic case.

Cheers,

Staszek