@Parameterized.Parameters(name = "{0}({1},{2}) = {3}")
        public static Iterable<Object[]> data() {
            return new ArrayList<>(Arrays.asList(new Object[][]{
                    {Operator.addAll, null, null, null},
                    {Operator.addAll, new HashMap<String,Integer>() {{ put("a", 1); }}, null, new HashMap<String,Integer>() {{ put("a", 1); }}},
                    {Operator.addAll, null, new HashMap<String,Integer>() {{ put("a", 1); }}, new HashMap<String,Integer>() {{ put("a", 1); }}},
                    {Operator.addAll, new HashMap<String,Integer>() {{ put("a", 1); }}, new HashMap<String,Integer>() {{ put("b", 2); }}, new HashMap<String,Integer>() {{ put("a", 1); put("b", 2); }}},
                    {Operator.addAll, new HashMap<String,Integer>() {{ put("a", 1); }}, new HashMap<String,Integer>() {{ put("a", 2); }}, new HashMap<String,Integer>() {{ put("a", 2); }}},
            }));
        }
@author Stephen Mallette (http://stephen.genoprime.com)
gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/process/traversal/OperatorTest.java