void putValue(long key, Boolean value) {
			cacheMap.put(key, value);
			if (value != null) {
				--outstandingRequestCount;
			}
			else {
				++outstandingRequestCount;
			}
		}
Put datatype pair equivalence state into cache. A null value is used to
indicate an equivalence check will be determined and another call made to
this method to update the cache with the equivalence state.

@param key   datatype identity pair (see
             {@link DataTypeManagerDB#getEquivalenceKey(DataTypeDB, DataType)}
@param value equivalence state (specify {@code null} to indicate equivalence
             determination is in-progress)
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/database/data/DataTypeManagerDB.java