How can I check if a playa field is empty?

Question

I have a playa field product_videos and am using the following conditional to check if it is empty:

{if product_videos:total_children > 0}
  //do something
{/if}

This seems pretty straight forward to me, what am I missing?

I should add the result is that the code inside the conditional never appears despite there being entries.

I have also tried:

{if "{exp:playa:total_children field='product_videos'}"}
  //do something
{/if}

which is listed as a correct answer in this SO question, this results in a php error:

A PHP Error was encountered Severity: User Warning

Message: Invalid EE Conditional Variable: {if "exp:playa:total_children entry_id="285" field='product_videos' var_prefix="playaDbig9XJo"}

Filename: libraries/Functions.php

Line Number: 2855

Answer 1

...And as soon as I write it down in a question, I figured out my mistake.

Correct solution for future visitors was:

{if "{product_videos:total_children}" > 0}
  //do something
{/if}