public static UnsupportedOperationException dataTypeOfVariableValueNotSupported(final Object val, final Exception rootCause) {
                return new UnsupportedOperationException(String.format("Graph variable value [%s] is of type %s is not supported", val, val.getClass()), rootCause);
            }
Gets the variables of the {@link Graph} as a {@code Map}.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/structure/Graph.java