title: Redshift COPY command raises error if S3 prefix does not exist
body: <p>When I run this COPY command:</p>
  
  <pre><code>COPY to_my_table (field1, field2, etc)
  FROM s3://my-service-f55b83j5vvkp/2018/09/03
  CREDENTIALS 'aws_iam_role=...'
  JSON 'auto' TIMEFORMAT 'auto';
  </code></pre>
  
  <p>I get this error:</p>
  
  <pre><code>The specified S3 prefix '2018/09/03' does not exist
  </code></pre>
  
  <p>Which makes sense, because my S3 bucket does not have any file in that specific prefix. However, this is part of a daily job to load data, where sometimes there's something to load, but some other times there's nothing to load.</p>
  
  <p>I checked the <a href="https://docs.aws.amazon.com/redshift/latest/dg/r_COPY.html" rel="nofollow noreferrer">COPY documentation</a> and it doesn't seem to be any way to avoid the error and just don't do anything if there are no objects under that prefix. Maybe I am missing something?</p>