@Override
	public ExternalReference getExternalReference(int opIndex) {
		validate(lock);
		Reference[] refs = refMgr.getReferencesFrom(address, opIndex);
		for (Reference element : refs) {
			if (element.isExternalReference()) {
				return (ExternalReference) element;
			}
		}
		return null;
	}
@see ghidra.program.model.listing.CodeUnit#addOperandReference(int,
     ghidra.program.model.address.Address,
     ghidra.program.model.symbol.RefType, SourceType)
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/database/code/CodeUnitDB.java