@Override
	String getCallingConventionName(byte id) throws IOException {
		if (id == DEFAULT_CALLING_CONVENTION_ID) {
			return Function.DEFAULT_CALLING_CONVENTION_STRING;
		}
		else if (id == UNKNOWN_CALLING_CONVENTION_ID) {
			return null;
		}
		populateCache();
		return callingConventionIDToNameMap.get(id);
	}
Remove next available free key value from freeKeySet.
@return the next available key. A negative value indicates that all allowed IDs have 
been used.
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/database/data/CallingConventionDBAdapterV0.java