mat-select-trigger is invisible if value is undefined or null

Bug, feature request, or proposal:

md-select-trigger is invisible if value is undefined or null when MD_PLACEHOLDER_GLOBAL_OPTIONS set to { float: 'always' }(use to show field name) i cant show ‘All’ or 'Please Select … ’ on the md-select

What is the expected behavior?

need a way to show hint text / empty option alternative text

What is the current behavior?

mat-select-trigger is invisible if value is undefined or null

What are the steps to reproduce?

https://stackblitz.com/edit/angular-material2-issue-vyqfqf

What is the use-case or motivation for changing an existing behavior?

use select as a list filter, or form control with a hint text

[hsinyu-chen]

now we have mat-label for this

<mat-form-field>
    <mat-label>Status</mat-label>
    <mat-select placeholder="Please Select">...</mat-select>
</mat-form-field>

@crisbeto I think you can close this issue

[ggranum]

@crisbeto, regarding when to show it: I would strongly argue that if the value for ‘trigger’ is not empty, it should always be displayed. The developer has full control over the value provided to the trigger, and with a simple ‘Placeholder will not display unless the triggerValue is empty’ in the docs, it’s clear enough what needs to be done.

If that is not an option, then it should be one, via a flag.

For a use case, I present a multi-select where ‘No Selection’ is allowed. I would like to display ‘All’, ‘Partial ({{count}})’ or ‘None’. I cannot display None, because the selection is empty thus the (empty) placeholder is displayed instead.