Fails on empty ECR repository

[pda]

For a brand new ECR repository which has never had an image pushed:

panic: InvalidParameter: 1 validation error(s) found.
--
  | - minimum field size of 1, DescribeImagesInput.ImageIds.
  |  
  |  
  | goroutine 1 [running]:
  | main.main()
  | /Users/pda/go/src/github.com/99designs/aws-ecr-gc/main.go:57 +0x308