Crash upon loading superflat preset: Non [a-z0-9_.-] character in namespace of location: 56*minecraft:stone

The bug

When Minecraft loads a custom superflat preset, the game can crash. This will happen if a semicolon ( ; ) is placed before the id of a block (eg. "minecraft:stone")

What I expected to happen was:

Minecraft would not crash, and revert to the "Classic Flat" preset, as it did in previous versions.

What actually happened was:

Minecraft crashed.

How to reproduce

1. Click "Create New World"

2. Select "Superflat" world type

3. Go into the the superflat customization settings

4. Put in the block id of a block (eg. "minecraft:stone")

5. Place a semicolon, as you would if you were going to specify a biome id

6. Specify another block id instead

7. Click "Use Preset"

-> ❌ Minecraft crashes

Crash report

---- Minecraft Crash Report ----
// Why is it breaking :(Time: 7/19/18 5:50 PM
Description: mouseClicked event handleri: Non [a-z0-9_.-] character in namespace of location: 56*minecraft:stone
	at pc.<init>(SourceFile:35)
	at pc.<init>(SourceFile:43)
	at btu.a(SourceFile:369)
	at cjb.a(SourceFile:70)
	at cjp$1.a(SourceFile:170)
	at cgj.mouseClicked(SourceFile:103)
	at chf.mouseClicked(SourceFile:46)
	at cfk.b(SourceFile:83)
	at cfk$$Lambda$932/348480093.run(Unknown Source)
	at cjs.a(SourceFile:430)
	at cfk.a(SourceFile:83)
	at cfk$$Lambda$779/1863346936.invoke(Unknown Source)
	at org.lwjgl.glfw.GLFWMouseButtonCallbackI.callback(GLFWMouseButtonCallbackI.java:36)
	at org.lwjgl.system.JNI.invokeV(Native Method)
	at org.lwjgl.glfw.GLFW.glfwPollEvents(GLFW.java:3029)
	at cfs.a(SourceFile:308)
	at cfi.c(SourceFile:872)
	at cfi.a(SourceFile:392)
	at net.minecraft.client.main.Main.main(SourceFile:144)
A detailed walkthrough of the error, its code path and all known details is as follows:
----------------------------------------------------------------------------------------- Head --
Thread: Client thread
Stacktrace:
	at pc.<init>(SourceFile:35)
	at pc.<init>(SourceFile:43)
	at btu.a(SourceFile:369)
	at cjb.a(SourceFile:70)
	at cjp$1.a(SourceFile:170)
	at cgj.mouseClicked(SourceFile:103)
	at chf.mouseClicked(SourceFile:46)
	at cfk.b(SourceFile:83)
	at cfk$$Lambda$932/348480093.run(Unknown Source)-- Affected screen --
Details:
	Screen name: cjp
Stacktrace:
	at cjs.a(SourceFile:430)
	at cfk.a(SourceFile:83)
	at cfk$$Lambda$779/1863346936.invoke(Unknown Source)
	at org.lwjgl.glfw.GLFWMouseButtonCallbackI.callback(GLFWMouseButtonCallbackI.java:36)
	at org.lwjgl.system.JNI.invokeV(Native Method)
	at org.lwjgl.glfw.GLFW.glfwPollEvents(GLFW.java:3029)
	at cfs.a(SourceFile:308)
	at cfi.c(SourceFile:872)
	at cfi.a(SourceFile:392)
	at net.minecraft.client.main.Main.main(SourceFile:144)-- System Details --
Details:
	Minecraft Version: 1.13
	Operating System: Windows 10 (amd64) version 10.0
	Java Version: 1.8.0_51, Oracle Corporation
	Java VM Version: Java HotSpot(TM) 64-Bit Server VM (mixed mode), Oracle Corporation
	Memory: 416502584 bytes (397 MB) / 704643072 bytes (672 MB) up to 1073741824 bytes (1024 MB)
	JVM Flags: 9 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xss1M -Xmx1G -XX:+UnlockExperimentalVMOptions -XX:+UseG1GC -XX:G1NewSizePercent=20 -XX:G1ReservePercent=20 -XX:MaxGCPauseMillis=50 -XX:G1HeapRegionSize=16M
	Launched Version: 1.13
	LWJGL: 3.1.6 build 14
	OpenGL: GeForce GTX 460M/PCIe/SSE2 GL version 4.5.0 NVIDIA 369.09, 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: Probably not. Jar signature remains and client brand is untouched.
	Type: Client (map_client.txt)
	Resource Packs: 
	Current Language: English (US)
	Profiler Position: N/A (disabled)
	CPU: 8x Intel(R) Core(TM) i7 CPU Q 740 @ 1.73GHz

Other

Doesn't necessarily seem to be a duplicate of MC-124123 (although probably strongly related). I reported this issue upon the recommendation of @unknown.