Boolean getValue(long key) {
			return cacheMap.get(key);
		}
Get the cached datatype pair equivalence

@param key datatype identity pair (see
           {@link DataTypeManagerDB#getEquivalenceKey(DataTypeDB, DataType)}
@return boolean equivalence or null if unknown or determination is
        in-progress
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/database/data/DataTypeManagerDB.java