Server crash when opening custom GUI

[Nikita Kalinin]

mod.js:

mod.addGui('mygui.js', 'crafting');
mod.addBlock('mytable.js', 'normal');

mygui.js:

name = 'mygui';
guiFile = '/gui/container/crafting_table.png'; // correct in 1.7.2

mytable.js:

name = 'mytable';
...
onActivated[0] = 'player.openGui("mygui", position); result = true;';
// Also tried "mymod:mygui".

When right-clicking by hand on mytable block game crashes:

java.lang.NullPointerException: Ticking memory connection
    at net.minecraft.network.NetHandlerPlayServer.func_147346_a(NetHandlerPlayServer.java:619)
    at net.minecraft.network.play.client.C08PacketPlayerBlockPlacement.func_148833_a(SourceFile:60)
    at net.minecraft.network.play.client.C08PacketPlayerBlockPlacement.func_148833_a(SourceFile:9)
    at net.minecraft.network.NetworkManager.func_74428_b(NetworkManager.java:211)
    at net.minecraft.network.NetworkSystem.func_151269_c(NetworkSystem.java:173)
    at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:680)
    at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:568)
    at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:186)
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:452)
    at net.minecraft.server.MinecraftServer$2.run(MinecraftServer.java:705)