Nitmetric fixes

src/metrics/detect_covariance.nit

@@ -473,19 +473,19 @@ redef class MType
 		end
 		#print "4.is {sub} a {sup}? <- no more resolution"
 
-		assert sub isa MClassType # It is the only remaining type
-
-		# A unfixed formal type can only accept itself
-		if sup isa MFormalType then
-			return false
+		if sub isa MBottomType or sub isa MErrorType then
+			return true
 		end
 
-		if sup isa MNullType then
-			# `sup` accepts only null
+		assert sub isa MClassType else print_error "{sub} <? {sup}" # It is the only remaining type
+
+		# Handle sup-type when the sub-type is class-based (other cases must have be identified before).
+		if sup isa MFormalType or sup isa MNullType or sup isa MBottomType or sup isa MErrorType then
+			# These types are not super-types of Class-based types.
 			return false
 		end
 
-		assert sup isa MClassType # It is the only remaining type
+		assert sup isa MClassType else print_error "got {sup} {sub.inspect}" # It is the only remaining type
 
 		# Now both are MClassType, we need to dig
 

src/metrics/static_types_metrics.nit

@@ -53,8 +53,9 @@ private class ATypeCounterVisitor
 	do
 		if n isa AAnnotation then return
 
-		if n isa AType then
-			var mclassdef = self.nclassdef.mclassdef.as(not null)
+		if n isa AType then do
+			var mclassdef = self.nclassdef.mclassdef
+			if mclassdef == null then break
 			var mtype = modelbuilder.resolve_mtype(mclassdef, n)
 			if mtype != null then
 				self.typecount.inc(mtype)