When a machine json file contains a part where its id is "minecraft:air@0", the machine will fail to load as minecraft:air is not recognised as a registry name. Allowing air blocks as part of a machine would be useful when you want to force an empty space in the structure.

The error:
[22:53:40] [Server thread/WARN] [modularmachinery]: Couldn't load machinery C:\Gameshit\MultiMC\instances\Binbao S8.minecraft\config\modularmachinery\machinery\soup_pot.json
com.google.gson.JsonParseException: Couldn't find block with registryName 'minecraft:air' !
at hellfirepvp.modularmachinery.common.util.BlockArray$BlockInformation.getDescriptor(BlockArray.java:353)
at hellfirepvp.modularmachinery.common.machine.DynamicMachine$MachineDeserializer.deserialize(DynamicMachine.java:243)
at hellfirepvp.modularmachinery.common.machine.DynamicMachine$MachineDeserializer.deserialize(DynamicMachine.java:147)
at com.google.gson.internal.bind.TreeTypeAdapter.read(TreeTypeAdapter.java:69)
at net.minecraft.util.JsonUtils.func_188173_a(SourceFile:492)
at net.minecraft.util.JsonUtils.func_193839_a(SourceFile:532)
at hellfirepvp.modularmachinery.common.machine.MachineLoader.loadMachines(MachineLoader.java:78)
at hellfirepvp.modularmachinery.common.machine.MachineRegistry.loadMachines(MachineRegistry.java:85)
at hellfirepvp.modularmachinery.common.command.CommandSyntax.func_184881_a(CommandSyntax.java:48)
at com.feed_the_beast.ftbutilities.ranks.CommandOverride.func_184881_a(CommandOverride.java:83)
at net.minecraft.command.CommandHandler.func_175786_a(CommandHandler.java:119)
at net.minecraft.command.CommandHandler.func_71556_a(CommandHandler.java:91)
at net.minecraft.network.NetHandlerPlayServer.func_147361_d(NetHandlerPlayServer.java:962)
at net.minecraft.network.NetHandlerPlayServer.func_147354_a(NetHandlerPlayServer.java:941)
at net.minecraft.network.play.client.CPacketChatMessage.func_148833_a(SourceFile:37)
at net.minecraft.network.play.client.CPacketChatMessage.func_148833_a(SourceFile:9)
at net.minecraft.network.PacketThreadUtil$1.run(SourceFile:13)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at net.minecraft.util.Util.func_181617_a(SourceFile:529)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:723)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:668)
at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:185)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526)
at java.lang.Thread.run(Thread.java:823)
com.google.gson.JsonParseException: Couldn't find block with registryName 'minecraft:air' !
at hellfirepvp.modularmachinery.common.util.BlockArray$BlockInformation.getDescriptor(BlockArray.java:353)
at hellfirepvp.modularmachinery.common.machine.DynamicMachine$MachineDeserializer.deserialize(DynamicMachine.java:243)
at hellfirepvp.modularmachinery.common.machine.DynamicMachine$MachineDeserializer.deserialize(DynamicMachine.java:147)
at com.google.gson.internal.bind.TreeTypeAdapter.read(TreeTypeAdapter.java:69)
at net.minecraft.util.JsonUtils.func_188173_a(SourceFile:492)
at net.minecraft.util.JsonUtils.func_193839_a(SourceFile:532)
at hellfirepvp.modularmachinery.common.machine.MachineLoader.loadMachines(MachineLoader.java:78)
at hellfirepvp.modularmachinery.common.machine.MachineRegistry.loadMachines(MachineRegistry.java:85)
at hellfirepvp.modularmachinery.common.command.CommandSyntax.func_184881_a(CommandSyntax.java:48)
at com.feed_the_beast.ftbutilities.ranks.CommandOverride.func_184881_a(CommandOverride.java:83)
at net.minecraft.command.CommandHandler.func_175786_a(CommandHandler.java:119)
at net.minecraft.command.CommandHandler.func_71556_a(CommandHandler.java:91)
at net.minecraft.network.NetHandlerPlayServer.func_147361_d(NetHandlerPlayServer.java:962)
at net.minecraft.network.NetHandlerPlayServer.func_147354_a(NetHandlerPlayServer.java:941)
at net.minecraft.network.play.client.CPacketChatMessage.func_148833_a(SourceFile:37)
at net.minecraft.network.play.client.CPacketChatMessage.func_148833_a(SourceFile:9)
at net.minecraft.network.PacketThreadUtil$1.run(SourceFile:13)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at net.minecraft.util.Util.func_181617_a(SourceFile:529)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:723)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:668)
at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:185)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526)
at java.lang.Thread.run(Thread.java:823)
com.google.gson.JsonParseException: Couldn't find block with registryName 'minecraft:air' !
at hellfirepvp.modularmachinery.common.util.BlockArray$BlockInformation.getDescriptor(BlockArray.java:353)
at hellfirepvp.modularmachinery.common.machine.DynamicMachine$MachineDeserializer.deserialize(DynamicMachine.java:243)
at hellfirepvp.modularmachinery.common.machine.DynamicMachine$MachineDeserializer.deserialize(DynamicMachine.java:147)
at com.google.gson.internal.bind.TreeTypeAdapter.read(TreeTypeAdapter.java:69)
at net.minecraft.util.JsonUtils.func_188173_a(SourceFile:492)
at net.minecraft.util.JsonUtils.func_193839_a(SourceFile:532)
at hellfirepvp.modularmachinery.common.machine.MachineLoader.loadMachines(MachineLoader.java:78)
at hellfirepvp.modularmachinery.common.machine.MachineRegistry.loadMachines(MachineRegistry.java:85)
at hellfirepvp.modularmachinery.common.command.CommandSyntax.func_184881_a(CommandSyntax.java:48)
at com.feed_the_beast.ftbutilities.ranks.CommandOverride.func_184881_a(CommandOverride.java:83)
at net.minecraft.command.CommandHandler.func_175786_a(CommandHandler.java:119)
at net.minecraft.command.CommandHandler.func_71556_a(CommandHandler.java:91)
at net.minecraft.network.NetHandlerPlayServer.func_147361_d(NetHandlerPlayServer.java:962)
at net.minecraft.network.NetHandlerPlayServer.func_147354_a(NetHandlerPlayServer.java:941)
at net.minecraft.network.play.client.CPacketChatMessage.func_148833_a(SourceFile:37)
at net.minecraft.network.play.client.CPacketChatMessage.func_148833_a(SourceFile:9)
at net.minecraft.network.PacketThreadUtil$1.run(SourceFile:13)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
at java.util.concurrent.FutureTask.run(FutureTask.java:266)
at net.minecraft.util.Util.func_181617_a(SourceFile:529)
at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:723)
at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:668)
at net.minecraft.server.integrated.IntegratedServer.func_71217_p(IntegratedServer.java:185)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526)
at java.lang.Thread.run(Thread.java:823)