fix bugs

1 files changed, 2 insertions, 1 deletions

diff --git a/src/world/proposal.js b/src/world/proposal.js
index 0969540..8baca06 100644
--- a/src/world/proposal.js
+++ b/src/world/proposal.js
@@ -57,6 +57,7 @@ import { pairs, deepEqual } from '../util.js';
 // check that two flags objects are compatible
 // flags are considered compatible if they do not have any common keys with different values
 function flags_compatible(a, b) {
+  if (a === undefined || b === undefined) { return true; }
   const keys = [...new Set(Object.keys(a).concat(Object.keys(b)))];
   return keys.reduce(
     (acc, key) => {
@@ -80,7 +81,7 @@ function lattice_change_conflict(a, b) {
   if (
     a.x === b.x && 
     a.y === b.y &&
-    (a.to != b.to || !flags_compatible(a.flags || {}, b.flags || {}))
+    (a.to != b.to || !flags_compatible((a.flags || {}), (b.flags || {})))
   ) {
     // conflict!
     return [true, false];