@Override
	public FunctionIterator getExternalFunctions() {
		return new FunctionIteratorDB(true, true);
	}
Get the function with the given key.
@param key ID of the function; ID is obtained by calling
Function.getID()
@return null if there is no function with the given key
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/database/function/FunctionManagerDB.java