Database queries fail silently if using DBTNG and a small typo is made

This isn't a 'bug' in behaviour per say, but an error I think that should be caught.

Calls to db_insert() and db_merge() silently fail when a small typo is made in calling them:

  $query = db_merge('tablename')
    ->key(array('colname', $fieldvalue))
    ->fields(array(
      'col1' => $val1,
      'col2' => $val2,
      'col3' => $val3,
    ))
    ->execute();

Note how in $key the fields are listed numerically, not associatively. The corrected line would look like:

    ->key(array('colname' => $fieldvalue))

If this programming error is made either in key() or fields(), the return value is a simple integer and the query fail with no error output or message in the site logs.