[MC-195582] Typing a colon twice or after a slash in chat when specifying a function/item/block/etc. in a command crashes the game

The game crashes when you type a colon twice or after a slash in a command in chat. The original is here, but was marked as fixed.

How to reproduce

Type a command in chat like /function :example:, clear @s minecraft/:, or execute as @e[type=minecraft::

Stack trace

20w29a: crash-2020-07-20_19.32.03-client.txt

Description: Rendering screen

java.lang.NullPointerException: Rendering screen
	at nu.a(SourceFile:74)
	at oh.b(SourceFile:132)
	at nu.a(SourceFile:76)
	at djz.a(SourceFile:134)
	at dkl.c(SourceFile:301)
	at dkl.b(SourceFile:155)
	at dkl.a(SourceFile:121)
	at dkl.a(SourceFile:107)
	at dkl.a(SourceFile:75)
	at dld.a(SourceFile:339)
	at dnf.a(SourceFile:202)
	at dzi.a(SourceFile:603)
	at djp.e(SourceFile:1020)
	at djp.e(SourceFile:653)
	at net.minecraft.client.main.Main.main(SourceFile:215)