fix secondary placeholder problem in chips

[dbwhddn10]

No description provided.

[topherfangio]

I need to dig into this a bit further before we can review it.

@dbwhddn10 Can you provide any additional info as to what this fixes? Ideally a description, test case and an issue # would be fantastic!

[ericgundrum]

@topherfangio, I have unit tests demonstrating issues #2770 and #4476. (Currently there are no unit tests for the placeholder feature of mdChips input.) I've created PR #6535 with those tests and the related fix. (The fix is a single line.)

I wrote a test to match the issue PR a5dba2a is trying to fix. However, there is much other mdChips code that fails to check if the ngModel is defined. There seems to be an inherent assumption that ngModel is defined or that catastrophic failure is preferred when it isn't. It may be better to separate this issue and PR from issues #2770 and #4476.

[EladBezalel]

@ericgundrum thanks.
@dbwhddn10 can you please rebase?
@topherfangio can you please investigate? :)

[topherfangio]

I'm going to go ahead and close this in favor of #6175 since it does the NPE check only and #6535 has already been merged.