test harness for isnull behaviour

mysql-test/suite/oqgraph/isnull.test

+--disable_warnings
+DROP TABLE IF EXISTS graph_base;
+DROP TABLE IF EXISTS graph;
+DROP TABLE IF EXISTS graph2;
+--enable_warnings
+
+# Create the backing store
+CREATE TABLE graph_base (
+    from_id INT UNSIGNED NOT NULL,
+    to_id INT UNSIGNED NOT NULL,
+    PRIMARY KEY (from_id,to_id),
+    INDEX (to_id)
+  ) ENGINE=MyISAM;
+
+
+CREATE TABLE graph (
+    latch   VARCHAR(32) NULL,
+    origid  BIGINT    UNSIGNED NULL,
+    destid  BIGINT    UNSIGNED NULL,
+    weight  DOUBLE    NULL,
+    seq     BIGINT    UNSIGNED NULL,
+    linkid  BIGINT    UNSIGNED NULL,
+    KEY (latch, origid, destid) USING HASH,
+    KEY (latch, destid, origid) USING HASH
+  ) ENGINE=OQGRAPH DATA_TABLE='graph_base' ORIGID='from_id', DESTID='to_id';
+
+
+INSERT INTO graph_base(from_id, to_id) VALUES (1,2), (2,1);
+INSERT INTO graph_base(from_id, to_id) VALUES (1,3), (3,1);
+INSERT INTO graph_base(from_id, to_id) VALUES (3,4), (4,3);
+INSERT INTO graph_base(from_id, to_id) VALUES (5,6), (6,5);
+
+select * from graph where latch is null;
+
+DROP TABLE graph_base;
+DROP TABLE graph;
+