Chisel for MC 1.12 depends on CTM.

People who don't read the CurseForge page, for whatever reason, frequently manage to install Chisel without installing CTM. (see, for example, #635, #601, #585, #572, #559.)

Sometimes, this gives an informative error message. For example, if you install only Chisel (and no other mods at all), Forge will tell you that you need CTM:

However, starting up with just one additional mod (Chisel + Tinker's Construct, for example) can cause Minecraft to crash before there's a chance to display the "CTM is missing" error. Instead, the user sees an error indicating a crash in some other mod:

java.lang.NullPointerException: The validated object is null
	at org.apache.commons.lang3.Validate.notNull(Validate.java:225)
	at org.apache.commons.lang3.Validate.notNull(Validate.java:206)
	at net.minecraft.util.registry.RegistrySimple.func_82595_a(SourceFile:35)
	at slimeknights.tconstruct.tools.ToolClientEvents.onModelBake(ToolClientEvents.java:89)

The lack of CTM isn't pointed out in the logs, either. For example, fml-client-latest.log doesn't mention the lack of ctm or connectedtexturesmod.

This is creating an (avoidable?) support burden on the Chisel team, and the Tinker's Construct team (see SlimeKnights/TinkersConstruct#3434, #3299, #3284, #3319, #3226, for example.)

The support burden may be lightened if Chisel is more aggressive about detecting the lack of CTM and failing very early. Adding CTM as a "Required Library" on CurseForge may also help. (Currently, CTMLib is listed as an Embedded Library), but there are no "Required Libraries" listed.)

Possibly related: #661 ?

Adding CTM as a "Required Library" on CurseForge may also help. (Currently, CTMLib is listed as an Embedded Library), but there are no "Required Libraries" listed.)

Pretend that tab doesn't exist. It's almost always wrong. Look at the individual files. It is listed.

Pretend that tab doesn't exist. It's almost always wrong. Look at the individual files. It is listed.

This is very good to know - thanks for pointing it out.

Also I'm pretty sure this is fixed in 5cb19a6

It is, yes. The problem with the old way is a forge bug that will probably never be fixed.