@Override
	public Address getAddress(Address sourceAddress) {
		Address destinationAddress = addressMap.get(sourceAddress);
		if (destinationAddress != null) {
			return destinationAddress;
		}
		throw new AddressTranslationException(
			"The specified source address never had an external address pair added to the translator.");
	}
ExternalsAddressTranslator is a translator that can be used for merging external functions and
labels. <br>
Important: Before using this with ProgramMerge you must add all the address pairs that
will translate the external address space address from the source program to the address
in the destination program.
Ghidra/Features/Base/src/main/java/ghidra/app/merge/listing/ExternalsAddressTranslator.java