Fix NPE when walking a missing node that will have missing properties

src/main/java/com/networknt/schema/TypeFactory.java

@@ -75,6 +75,11 @@ public static JsonType getSchemaNodeType(JsonNode node) {
      * @return the json type
      */
     public static JsonType getValueNodeType(JsonNode node, SchemaValidatorsConfig config) {
+        if (node == null) {
+            // This returns JsonType.UNKNOWN to be consistent with the behavior when
+            // JsonNodeType.MISSING
+            return JsonType.UNKNOWN;
+        }
         JsonNodeType type = node.getNodeType();
         switch (type) {
         case OBJECT:

src/test/java/com/networknt/schema/JsonWalkTest.java

@@ -2,6 +2,7 @@
 
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.MissingNode;
 import com.fasterxml.jackson.databind.node.ObjectNode;
 import com.networknt.schema.walk.JsonSchemaWalkListener;
 import com.networknt.schema.walk.WalkEvent;
@@ -16,6 +17,7 @@
 import java.util.Set;
 import java.util.TreeSet;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
 class JsonWalkTest {
@@ -110,6 +112,27 @@ void testWalkWithDifferentListeners() throws IOException {
                 + "}")));
     }
 
+    @Test
+    void testWalkMissingNodeWithPropertiesSchemaShouldNotThrow() {
+        String schemaContents = "{\n"
+                + "                \"type\": \"object\",\n"
+                + "                \"properties\": {\n"
+                + "                    \"field\": {\n"
+                + "                    \"anyOf\": [\n"
+                + "                        {\n"
+                + "                        \"type\": \"string\"\n"
+                + "                        }\n"
+                + "                    ]\n"
+                + "                    }\n"
+                + "                }\n"
+                + "            }";
+
+        JsonSchemaFactory factory = JsonSchemaFactory.getInstance(SpecVersion.VersionFlag.V7);
+        JsonSchema schema = factory.getSchema(schemaContents);
+        JsonNode missingNode = MissingNode.getInstance();
+        assertDoesNotThrow(() -> schema.walk(missingNode, true));
+    }
+
     private InputStream getSchema() {
         return getClass().getClassLoader().getResourceAsStream("schema/walk-schema.json");
     }