A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

-- Head --
Thread: Client thread
Stacktrace:
	at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:864)
	at net.minecraftforge.registries.ForgeRegistry.add(ForgeRegistry.java:272)
	at net.minecraftforge.registries.ForgeRegistry.add(ForgeRegistry.java:266)
	at net.minecraftforge.registries.ForgeRegistry.register(ForgeRegistry.java:110)
	at gunn.modcurrency.mod.block.ModBlocks.registerItems(ModBlocks.java:31)
	at net.minecraftforge.fml.common.eventhandler.ASMEventHandler_10_ModBlocks_registerItems_Register.invoke(.dynamic)
	at net.minecraftforge.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:90)
	at net.minecraftforge.fml.common.eventhandler.EventBus$1.invoke(EventBus.java:143)
	at net.minecraftforge.fml.common.eventhandler.EventBus.post(EventBus.java:179)
	at net.minecraftforge.registries.GameData.fireRegistryEvents(GameData.java:693)
	at net.minecraftforge.registries.GameData.fireRegistryEvents(GameData.java:673)
	at net.minecraftforge.fml.common.Loader.preinitializeMods(Loader.java:605)
	at net.minecraftforge.fml.client.FMLClientHandler.beginMinecraftLoading(FMLClientHandler.java:266)
	at net.minecraft.client.Minecraft.init(Minecraft.java:503)

-- Initialization --
Details:
Stacktrace:
	at net.minecraft.client.Minecraft.run(Minecraft.java:411)
	at net.minecraft.client.main.Main.main(Main.java:118)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at net.minecraft.launchwrapper.Launch.launch(Launch.java:135)
	at net.minecraft.launchwrapper.Launch.main(Launch.java:28)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at net.minecraftforge.gradle.GradleStartCommon.launch(GradleStartCommon.java:97)
	at GradleStart.main(GradleStart.java:26)

-- System Details --
Details:
	Minecraft Version: 1.12
	Operating System: Windows 10 (amd64) version 10.0
	Java Version: 1.8.0_121, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 686462504 bytes (654 MB) / 956301312 bytes (912 MB) up to 3790077952 bytes (3614 MB)
	JVM Flags: 0 total;
	IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
	FML: MCP 9.40 Powered by Forge 14.21.1.2387 6 mods loaded, 6 mods active
	States: 'U' = Unloaded 'L' = Loaded 'C' = Constructed 'H' = Pre-initialized 'I' = Initialized 'J' = Post-initialized 'A' = Available 'D' = Disabled 'E' = Errored
	UCH	minecraft{1.12} [Minecraft] (minecraft.jar)
	UCH	mcp{9.19} [Minecraft Coder Pack] (minecraft.jar)
	UCH	FML{8.0.99.99} [Forge Mod Loader] (forgeSrc-1.12-14.21.1.2387.jar)
	UCH	forge{14.21.1.2387} [Minecraft Forge] (forgeSrc-1.12-14.21.1.2387.jar)
	UCH	modcurrency{1.12-1.1.2} [Good Ol' Currency Mod] (Currency-Mod_main)
	UCH	jei{4.6.0.61} [Just Enough Items] (jei_1.12-4.6.0.61.jar)
	Loaded coremods (and transformers):
	GL info: ' Vendor: 'NVIDIA Corporation' Version: '4.5.0 NVIDIA 382.53' Renderer: 'GeForce GTX 970M/PCIe/SSE2'
	Launched Version: 1.12
	LWJGL: 2.9.4
	OpenGL: GeForce GTX 970M/PCIe/SSE2 GL version 4.5.0 NVIDIA 382.53, NVIDIA Corporation
	GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Shaders are available because OpenGL 2.1 is supported.
VBOs are available because OpenGL 1.5 is supported.

	Using VBOs: Yes
	Is Modded: Definitely; Client brand changed to 'fml,forge'
	Type: Client (map_client.txt)
	Resource Packs:
	Current Language: English (US)
	Profiler Position: N/A (disabled)
	CPU: 8x Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHz
[10:41:20] [main/INFO] [STDOUT]: [net.minecraft.init.Bootstrap:printToSYSOUT:629]: #@!@# Game crashed! Crash report saved to: #@!@# D:\Projects\Minecraft\Mod Development\Currency-Mod\run\.\crash-reports\crash-2017-07-01_10.41.20-client.txt
Disconnected from the target VM, address: '127.0.0.1:50696', transport: 'socket'

Process finished with exit code -1