Check for null value before using in. (#176)

* Check for null value before using `in`.

* Add test for schema with null value.

Author: William P. Riley-Land

index.js

@@ -188,6 +188,7 @@ function inferTypeByKeyword (schema) {
 }
 
 function hasAnyOf (schema) {
+  if (!schema) { return false }
   if ('anyOf' in schema) { return true }
 
   var objectKeys = Object.keys(schema)

test/anyof.test.js

@@ -231,3 +231,20 @@ test('object with field with type union of multiple objects', (t) => {
     t.fail()
   }
 })
+
+test('null value in schema', (t) => {
+  t.plan(0)
+
+  const schema = {
+    title: 'schema with null child',
+    type: 'string',
+    nullable: true,
+    enum: [null]
+  }
+
+  try {
+    build(schema)
+  } catch (e) {
+    t.fail()
+  }
+})