Docs: custom telephone number input control not working

[Tachionstrahl]

Description

On the doc page "Creating a custom form field control" the first example is not working.
It just shows an empty example box. In StackBlitz the example works.

Screenshot

Steps to reproduce

Visit https://material.angular.io/guide/creating-a-custom-form-field-control

Environment

Tested with Chrome Version 80.0.3987.87 (64-Bit) and Firefox 68.4.2esr (64-Bit)

[Splaktar]

Due to

ERROR Error: NullInjectorError: No provider for FormBuilder!
    at NullInjector.get (core.js:1050) [angular]
    at R3Injector.get (core.js:16521) [angular]
    at R3Injector.get (core.js:16521) [angular]
    at R3Injector.get (core.js:16521) [angular]
    at NgModuleRef$1.get (core.js:35539) [angular]
    at R3Injector.get (core.js:16521) [angular]
    at NgModuleRef$1.get (core.js:35539) [angular]
    at Object.get (core.js:33331) [angular]
    at getOrCreateInjectable (core.js:5453) [angular]
    at ɵɵdirectiveInject (core.js:20759) [angular]
    at NodeInjectorFactory.MyTelInput_Factory [as factory] (form-field.js:367) [angular]

[Splaktar]

Thank you for the report! PR #719 will fix this.