static byte getRefLevel(RefType rt) {
		if (rt == RefType.EXTERNAL_REF) {
			return (byte) SymbolUtilities.EXT_LEVEL;
		}
		if (rt.isCall()) {
			return (byte) SymbolUtilities.SUB_LEVEL;
		}
		if (rt.isData() || rt.isIndirect()) {
			return (byte) SymbolUtilities.DAT_LEVEL;
		}
		if (rt.isFlow()) {
			return (byte) SymbolUtilities.LAB_LEVEL;
		}
		return (byte) SymbolUtilities.UNK_LEVEL;
	}
Construct reference list for existing record
@param rec existing refList record
@param adapter entry record storage adapter
@param addrMap address map for encoding/decoding addresses
@param program associated Program
@param cache RefList object cache
@param isFrom true for from-adapter use, false for to-adapter use
@throws IOException if database IO error occurs
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/database/references/BigRefListV0.java