When upgrading to 6.x-3.0-alpha5, I get the following error:

warning: array_merge() [function.array-merge]: Argument #2 is not an array in /home/byronnsw/domains/dev.byron.nsw.gov.au/public_html/update.php on line 173.
warning: Invalid argument supplied for foreach() in /home/byronnsw/domains/dev.byron.nsw.gov.au/public_html/update.php on line 340.

This is similar to the closed issue https://www.drupal.org/node/1888756 .

I have encountered this will other modules. It seems to often be the result of not declaring an array to return. The only difference in the .install files between alpha4(which works) and alpha5 is the last few lines as below.

/**
 * Upgrade to beta1 or aplha5 (depending on Simplenews) 
 */
function simplenews_statistics_update_6303() {
  // Remove all statistics for nodes that don't exist anymore
  $query = 'DELETE FROM {simplenews_statistics} WHERE nid NOT IN (SELECT nid FROM {node})';
  db_query($query);
  $query = 'DELETE FROM {simplenews_statistics_clicks} WHERE nid NOT IN (SELECT nid FROM {node})';
  db_query($query);
  $query = 'DELETE FROM {simplenews_statistics_opens} WHERE nid NOT IN (SELECT nid FROM {node})';
  db_query($query);
}