public Class<?> getAllContainedElementsClass() {
        if (allContainedElementsSameClass()) {
            return allContainedElementsClass;
        } else {
            return null;
        }
    }
@return the class of all contained elements/objects if it is guaranteed that all are of the same type/class (but not
necessarily, i.e., they can have the same type/class, but we may return null here if it was not analysed/identified).
If no common class was identified, then null is returned.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/util/BulkSet.java