I keep getting "null" for 'Key' when following the instructions given here: https://docs.statamic.com/assets#s3-driver

This throws an error:

InvalidArgumentException in Validator.php line 65: Found 2 errors while validating the input provided for the GetObject operation: [Key] is missing and is a required parameter [Key] expected string length to be >= 1, but found string length of 0

I'm not leaving this field empty so I'm not understanding why it's returning NULL?