If there is only one result expected we will still keep iterating over the list, worth considering reversing the check to

if (versionedFeatureDef.getVisibility() == Visibility.PUBLIC) {
return versionedFeatureDef;
// OR
result = versionedFeatureDef;
break;
}

thanks will do

not sure on the logic here, if a public feature is found return that feature, but if one isn't it still sets the result to the feature, I am assuming that this line (and the break) are not needed or it will just look at the first feature and return it regardless of whether it is public

no longer create a "result" variable - makes no sense... - added the possiblibilty of returning null in javadoc

If we get to this point then we have not found a public feature, is this an error case?

not an error but return null

result is never used is it (now the method returns null at the end)?

removed result

do we need to null check firstChild?

If we do, we need to check whether the list is empty before calling get(0) because that will throw an exception.

Agreed made changes to check

Please add more documentation about what each of these fields means and what data it contains.

These fields look like they are used in other places, but here seems like the most logical place to document them.

There's a little bit of doc on the constructor and it sounds like missingPlaforms and missingBasePlatforms are completely different? That could do with a better explanation and possibly missingBasePlatforms should be renamed.

yes tried to add javadoc - one is simply a missspelling of a platform name - one is related to a base name like MP or jakarta realted to a versionless feature - if they can't be derived up front - its an error, and the reason the feature isn't resolved.

What does it mean for a platform to be "missing"?

Will a platform name only be in this set if the user requested it explicitly?