Index: src/wp-includes/js/wp-api.js
===================================================================
--- src/wp-includes/js/wp-api.js	(revision 42657)
+++ src/wp-includes/js/wp-api.js	(working copy)
@@ -848,7 +848,7 @@
 					model.unset( 'slug' );
 				}
 
-				if ( _.isFunction( model.nonce ) && ! _.isUndefined( model.nonce() ) && ! _.isNull( model.nonce() ) ) {
+				if ( _.isFunction( model.nonce ) && ! _.isEmpty( model.nonce() ) ) {
 					beforeSend = options.beforeSend;
 
 					// @todo enable option for jsonp endpoints
@@ -1466,6 +1466,7 @@
 	 * Initialize the wp-api, optionally passing the API root.
 	 *
 	 * @param {object} [args]
+	 * @param {string} [args.nonce] The nonce. Optional, defaults to wpApiSettings.nonce.
 	 * @param {string} [args.apiRoot] The api root. Optional, defaults to wpApiSettings.root.
 	 * @param {string} [args.versionString] The version string. Optional, defaults to wpApiSettings.root.
 	 * @param {object} [args.schema] The schema. Optional, will be fetched from API if not provided.
@@ -1474,7 +1475,7 @@
 		var endpoint, attributes = {}, deferred, promise;
 
 		args                      = args || {};
-		attributes.nonce          = args.nonce || wpApiSettings.nonce || '';
+		attributes.nonce          = _.isString( args.nonce ) ? args.nonce : ( wpApiSettings.nonce || '' );
 		attributes.apiRoot        = args.apiRoot || wpApiSettings.root || '/wp-json';
 		attributes.versionString  = args.versionString || wpApiSettings.versionString || 'wp/v2/';
 		attributes.schema         = args.schema || null;