[server] guard against the null module being added as a dependency

closes #11463

src/compiler/server.ml

@@ -312,7 +312,11 @@ let check_module sctx ctx m p =
 		in
 		let check_dependencies () =
 			PMap.iter (fun _ (sign,mpath) ->
-				let m2 = (com.cs#get_context sign)#find_module mpath in
+				let m2 = try
+					(com.cs#get_context sign)#find_module mpath
+				with Not_found ->
+					die (Printf.sprintf "Could not find dependency %s of %s in the cache" (s_type_path mpath) (s_type_path m.m_path)) __LOC__;
+				in
 				match check m2 with
 				| None -> ()
 				| Some reason -> raise (Dirty (DependencyDirty(m2.m_path,reason)))

src/core/tFunctions.ml

@@ -283,7 +283,7 @@ let null_abstract = {
 }
 
 let add_dependency ?(skip_postprocess=false) m mdep =
-	if m != null_module && (m.m_path != mdep.m_path || m.m_extra.m_sign != mdep.m_extra.m_sign) then begin
+	if m != null_module && mdep != null_module && (m.m_path != mdep.m_path || m.m_extra.m_sign != mdep.m_extra.m_sign) then begin
 		m.m_extra.m_deps <- PMap.add mdep.m_id (mdep.m_extra.m_sign, mdep.m_path) m.m_extra.m_deps;
 		(* In case the module is cached, we'll have to run post-processing on it again (issue #10635) *)
 		if not skip_postprocess then m.m_extra.m_processed <- 0