ST6RI-951 NullPointerException in FeatureAdapter#getTypes when a feature chain is partially unresolved

[adaussy]

This PR revises FeatureAdapter#getTypes(...) so it doesn't throw NullPointerException when deriving the type of a Feature whose typingFeatures() result contains a null entry.

Background

The implementation of Feature::typingFeatures includes the last chaining feature when the feature has an owned FeatureChaining. In Feature_typingFeatures_InvocationDelegate:

EList<Feature> chainingFeatures = self.getChainingFeature();
if (!chainingFeatures.isEmpty()) {
    Feature lastChainingFeature = chainingFeatures.get(chainingFeatures.size() - 1);
    if (!typingFeatures.contains(lastChainingFeature)) {
        typingFeatures.add(lastChainingFeature);
    }
}

However, FeatureChaining::getChainingFeature is a reference. During import or before reference resolution completes, that reference can legitimately be unresolved or absent from the in-memory model. In that state, self.getChainingFeature() can contain a null value. That null then becomes part of the typingFeatures() result.

The problem is not that typingFeatures() contains null by itself. The problem is that FeatureAdapter::getTypes assumes every entry is non-null and recursively processes it as a real Feature.

Change

Update FeatureAdaper::getTypes to check for null as it iterates over typing Features.