[changed] null is not considered an empty value for isValid

Author: jquense

src/mixed.js

@@ -327,7 +327,7 @@ SchemaType.prototype = {
       name: 'oneOf',
       test(value) {
         let valids = this.schema._whitelist
-        if (valids.length && !(valids.has(value) || isAbsent(value)))
+        if (valids.length && !(value === undefined || valids.has(value)))
           return this.createError({
             params: {
               values: valids.values().join(', ')

test/mixed.js

@@ -71,21 +71,27 @@ describe( 'Mixed Types ', function(){
   })
 
   it('should ignore absent values', function(){
-    return  Promise.all([
+    return Promise.all([
       mixed()
         .oneOf(['hello'])
         .isValid(undefined)
         .should.eventually.equal(true),
       mixed()
+        .nullable()
         .oneOf(['hello'])
-        .required()
         .isValid(null)
         .should.eventually.equal(false),
-      string()
+      mixed()
+        .oneOf(['hello'])
+        .required()
+        .isValid(undefined)
+        .should.eventually.equal(false),
+      mixed()
         .nullable()
         .oneOf(['hello'])
+        .required()
         .isValid(null)
-        .should.eventually.equal(true)
+        .should.eventually.equal(false)
     ])
   })