public void finish() {
		if (finished) {
			return;
		}
		symbols = unmodifiableSymbols;
		finished = true;
	}
Trim leading and trailing whitespace, and make the sentential immutable
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/app/plugin/assembler/sleigh/grammars/AssemblySentential.java