code: public UnfilledDependency replaceObject(IndexedPredicate newObject) {
      return new UnfilledDependency(subject, subjectSyntax, subjectFunctionVarIndex,
          subjectArgIndex, newObject, -1);
    }
docs: Returns a new UnfilledDependency whose object is {@code newObject}
  and whose subject is equal to {@code this}'s subject.
  
  @param newObject
  @return