[js] Normalize empty custom locator results

javascript/selenium-webdriver/lib/webdriver.js

@@ -1045,6 +1045,9 @@ class WebDriver {
   async findElementInternal_(locatorFn, context) {
     let result = await locatorFn(context)
     if (Array.isArray(result)) {
+      if (result.length === 0) {
+        throw new NoSuchElementError('Cannot locate an element with provided parameters')
+      }
       result = result[0]
     }
     if (!(result instanceof WebElement)) {
@@ -1088,7 +1091,15 @@ class WebDriver {
    * @private
    */
   async findElementsInternal_(locatorFn, context) {
-    const result = await locatorFn(context)
+    let result
+    try {
+      result = await locatorFn(context)
+    } catch (ex) {
+      if (ex instanceof NoSuchElementError) {
+        return []
+      }
+      throw ex
+    }
     if (result instanceof WebElement) {
       return [result]
     }

javascript/selenium-webdriver/test/lib/webdriver_test.js

@@ -726,6 +726,15 @@ describe('WebDriver', function () {
           assert.strictEqual('Custom locator did not return a WebElement', e.message)
         })
     })
+
+    it('customLocatorThrowsNoSuchElementErrorForEmptyArray', function () {
+      const driver = new FakeExecutor().createDriver()
+      return driver
+        .findElement((_) => [])
+        .then(assert.fail, function (e) {
+          assertIsInstance(error.NoSuchElementError, e)
+        })
+    })
   })
 
   describe('findElements', function () {
@@ -854,6 +863,20 @@ describe('WebDriver', function () {
         })
         .then((actual) => assert.deepStrictEqual(['one', 'two'], actual))
     })
+
+    it('customLocatorReturnsEmptyArrayForNoSuchElementError', function () {
+      const driver = new FakeExecutor().createDriver()
+      return driver
+        .findElements((_) => {
+          throw new error.NoSuchElementError()
+        })
+        .then((actual) => assert.deepStrictEqual([], actual))
+    })
+
+    it('customLocatorPropagatesUnexpectedErrors', function () {
+      const driver = new FakeExecutor().createDriver()
+      return driver.findElements(throwStubError).then(assert.fail, assertIsStubError)
+    })
   })
 
   describe('sendKeys', function () {