Index: ps/trunk/binaries/data/mods/public/simulation/components/GuiInterface.js
===================================================================
--- ps/trunk/binaries/data/mods/public/simulation/components/GuiInterface.js
+++ ps/trunk/binaries/data/mods/public/simulation/components/GuiInterface.js
@@ -650,7 +650,11 @@
  */
 GuiInterface.prototype.GetIncomingAttacks = function(player)
 {
-	return QueryPlayerIDInterface(player, IID_AttackDetection).GetIncomingAttacks();
+	let cmpAttackDetection = QueryPlayerIDInterface(player, IID_AttackDetection);
+	if (!cmpAttackDetection)
+		return [];
+
+	return cmpAttackDetection.GetIncomingAttacks();
 };
 
 /**
@@ -658,7 +662,8 @@
  */
 GuiInterface.prototype.GetNeededResources = function(player, data)
 {
-	return QueryPlayerIDInterface(data.player !== undefined ? data.player : player).GetNeededResources(data.cost);
+	let cmpPlayer = QueryPlayerIDInterface(data.player !== undefined ? data.player : player);
+	return cmpPlayer ? cmpPlayer.GetNeededResources(data.cost) : {};
 };
 
 /**
@@ -766,7 +771,11 @@
 
 GuiInterface.prototype.GetAvailableFormations = function(player, wantedPlayer)
 {
-	return QueryPlayerIDInterface(wantedPlayer).GetFormations();
+	let cmpPlayer = QueryPlayerIDInterface(wantedPlayer);
+	if (!cmpPlayer)
+		return [];
+
+	return cmpPlayer.GetFormations();
 };
 
 GuiInterface.prototype.GetFormationRequirements = function(player, data)
@@ -1956,7 +1965,11 @@
 
 GuiInterface.prototype.GetTradingGoods = function(player)
 {
-	return QueryPlayerIDInterface(player).GetTradingGoods();
+	let cmpPlayer = QueryPlayerIDInterface(player);
+	if (!cmpPlayer)
+		return [];
+
+	return cmpPlayer.GetTradingGoods();
 };
 
 GuiInterface.prototype.OnGlobalEntityRenamed = function(msg)
Index: ps/trunk/binaries/data/mods/public/simulation/components/PlayerManager.js
===================================================================
--- ps/trunk/binaries/data/mods/public/simulation/components/PlayerManager.js
+++ ps/trunk/binaries/data/mods/public/simulation/components/PlayerManager.js
@@ -91,11 +91,11 @@
 	if (id in this.playerEntities)
 		return this.playerEntities[id];
 
-	// All players at or below ID 0 get gaia-level data. (Observers for example)
-	if (id <= 0)
-		return this.playerEntities[0];
+	// Observers don't have player data.
+	if (id == INVALID_PLAYER)
+		return INVALID_ENTITY;
 
-	var stack = new Error().stack.trimRight().replace(/^/mg, '  '); // indent each line
+	let stack = new Error().stack.trimRight().replace(/^/mg, '  '); // indent each line
 	warn("GetPlayerByID: no player defined for id '"+id+"'\n"+stack);
 
 	return INVALID_ENTITY;