$StaplerConverterImpl is invoked with unexpected arguments

[daniel-beck]

Given a databound type with a List<SomeClass> property, and SomeClass$StaplerConverterImpl existing, this code appears to invoke the converter, passing the List<SomeClass> object, asking to get a SomeClass, when exporting a configuration:

configuration-as-code-plugin/plugin/src/main/java/io/jenkins/plugins/casc/impl/configurators/DataBoundConfigurator.java

Lines 300 to 304 in 8264363

	final Attribute a = createAttribute(names[i], TypePair.of(p));
	if (a != null) {
	Object value = a.getValue(instance);
	if (value != null) {
	Object converted = Stapler.CONVERT_UTILS.convert(value, a.getType());

The correct behavior is implementation-dependent, but likely involves returning a List<?>.

This seems unexpected. My expectation was that the converter is invoked once for each SomeClass list entry.

See https://github.com/jenkinsci/matrix-auth-plugin/pull/145/files#diff-a714ec3c04d484b6a8bb5fa7b0bf64cf3ebb61dfc095fb4b826cdac479c257bfR62-R69 for an example of this in matrix-auth.