code: public boolean isAssigned(PropertyFilter<S> propFilter) {
          if (propFilter.isConstant()) {
              return true;
          }
  
          Map<PropertyFilter<S>, Object> map = mValueMap;
  
          if (map == null) {
              FilterValues<S> prevValues = mPrevValues;
              if (prevValues == null) {
                  return false;
              }
  
              if (prevValues.mCurrentProperty.getPreviousRemaining() < 3) {
                  // Map would have few values in it, so don't bother building it.
  
                  do {
                      if (propFilter == prevValues.mCurrentProperty.getPropertyFilter()) {
                          return true;
                      }
                      prevValues = prevValues.mPrevValues;
                  } while (prevValues != null);
  
                  return false;
              }
  
              map = buildValueMap();
          }
  
          return map.containsKey(propFilter);
      }
docs: Returns true if a value is assigned to the given PropertyFilter.