public Collection<AssemblyNonTerminal> getNullable() {
		return Collections.unmodifiableSet(nullable);
	}
Get the nullable set

<p>
That is the set of all non-terminals, which through some derivation, can produce epsilon.

@return the set
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/app/plugin/assembler/sleigh/parse/AssemblyFirstFollow.java