2 files changed, 17 insertions(+), 1 deletions(-)

M lib/dhall/builtins.rb
M test/test_typechecker.rb

@@ 27,7 27,7 @@ module Dhall
 			if (unfilled = unfill).class != self.class
 				unfilled.as_json
 			else
-				self.class.name.split(/::/).last.tr("_", "/")
+				self.class.name&.split(/::/)&.last&.tr("_", "/").to_s
 			end
 		end
 

@@ 90,4 90,20 @@ class TestTypechecker < Minitest::Test
 			).annotate(context).type
 		)
 	end
+
+	def test_unknown_expression
+		assert_raises TypeError do
+			Dhall::TypeChecker.for(Class.new.new).annotate(
+				Dhall::TypeChecker::Context.new
+			)
+		end
+	end
+
+	def test_unknown_builtin
+		assert_raises TypeError do
+			Dhall::TypeChecker.for(Class.new(Dhall::Builtin).new).annotate(
+				Dhall::TypeChecker::Context.new
+			)
+		end
+	end
 end