default VertexProperty.Cardinality getCardinality(final String key) {
                return VertexProperty.Cardinality.list;
            }
Gets the {@link VertexProperty.Cardinality} for a key.  By default, this method will return
{@link VertexProperty.Cardinality#list}.  Implementations that employ a schema can consult it to
determine the {@link VertexProperty.Cardinality}.  Those that do no have a schema can return their
default {@link VertexProperty.Cardinality} for every key.
<p/>
Note that this method is primarily used by TinkerPop for internal usage and may not be suitable to
reliably determine the cardinality of a key. For some implementation it may offer little more than a
hint on the actual cardinality. Generally speaking it is likely best to drop down to the API of the
{@link Graph} implementation for any schema related queries.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/Graph.java