PerFieldAnalyzerWrapper.GetTokenStream throws NullReferenceException when first arg is null. It does not default.

var english = new EnglishAnalyzer(Lucene.Net.Util.LuceneVersion.LUCENE_48);

var whitespace = new WhitespaceAnalyzer(Lucene.Net.Util.LuceneVersion.LUCENE_48);

var pf = new PerFieldAnalyzerWrapper(english, new Dictionary<string, Analyzer>() { { "foo", whitespace }});

var test1 = english.GetTokenStream(null, "test"); // Does not throw

var test2 = pf.GetTokenStream("", "test"); // works

var test3 = pf.GetTokenStream(null, "test"); // Throws NullReferenceException

I don't think I'm doing anything wrong, but the last line crashes with the abovementioned exception.