EC2 volumes - attach_time is null

This has been split out from #960265, so it can be solved individually:

Description: attachTime is NULL when some attachment exist + workaround from case (2)

Code
 my $aws = Net::Amazon::EC2->new (...);
 my $vol = "vol-00000008";
 my @avol = ($vol);
 my $p_avol = \@avol;
 my $rtn=$aws->ec2->describe_volumes(VolumeId => $p_avol);

 response:
  <DescribeVolumesResponse xmlns="http://ec2.amazonaws.com/doc/2009-11-30/">
   <requestId>...</requestId>
   <volumeSet>
    <item>
     <status>in-use (nova, host1, i-00000001[host1], /dev/sdf)</status>
     <availabilityZone>nova</availabilityZone>
     <displayName/>
     <volumeId>vol-00000008</volumeId>
     <displayDescription/>
     <attachmentSet>
      <item>
       <status>attached</status>
       <attachTime/>
       <instanceId>i-00000037</instanceId>
       <volumeId>vol-00000008</volumeId>
       <deleteOnTermination>false</deleteOnTermination>
       <device>/dev/sdf</device>
      </item>
     </attachmentSet>
     <snapshotId/>
     <createTime>2012-03-12T10:43:31Z</createTime>
     <size>15</size>
    </item>
   </volumeSet>
  </DescribeVolumesResponse>

 error message from Net::Amazon::EC2:
  Attribute (attach_time) does not pass the type constraint because: Validation failed for 'Str' with value HASH(0x3ce5d10) at /usr/share/perl5/vendor_perl/Net/Amazon/EC2.pm line 391

 SQL:
  [root@host1 nova]# mysql -u.... -p..... nova -e "select attach_time,id from volumes;"
  +-------------+----+
  | attach_time | id |
  +-------------+----+
  | NULL | 1 |
  | NULL | 2 |
  | NULL | 3 |
  | NULL | 4 |
  | NULL | 5 |
  | NULL | 6 |
  | NULL | 7 |
  | NULL | 8 |
  | NULL | 9 |
  | NULL | 10 |
  | NULL | 11 |
  | NULL | 12 |
  | NULL | 13 |
  | NULL | 14 |
  | NULL | 15 |
  +-------------+----+