libvirt users - Oct 2014 - Question about vnc connection password set to empty

Hello, everybody

here I have a question about graphical buffers for rhel7. Thanks so much in
advance who can give me some suggestions about that.

When I try to do regression for
bug859317(https://bugzilla.redhat.com/show_bug.cgi?id=859317) on RHEL7， I found
that guest could be connected success with virt-viewer when set/update the
graphics passwd to empty.
But according to comment 2 in this bug, libvirt will blocks all access to the
VNC server when set a password to empty.
So could you please help us check is it acceptable on RHEL7?

Below is my test steps on RHEL7:

Version-Release number of selected component (if applicable):
libvirt-1.2.8-3.el7.x86_64
qemu-kvm-rhev-2.1.0-5.el7.x86_64
kernel-3.10.0-150.el7.x86_64


How reproducible:
100%

Steps to Reproduce:
 1. Define guest with a graphics device like:
    .........................................
      <graphics type='vnc' port='-1' autoport='yes'
passwd=""/>
    .........................................

 2. Connecting with vncviewer or virt-viewer .
      # virsh start dom2

      # virsh dumpxml dom2 --security-info |grep graphics
    <graphics type='vnc' port='5900' autoport='yes'
listen='127.0.0.1' passwd=''>
    </graphics>

      # virt-viewer dom2
   connect the guest success with empty password

 3. The problem can be reproduced when changed the graphics passwd from an
non-empty to an empty
    # virsh dumpxml dom2 --security-info |grep graphics
    <graphics type='vnc' port='5900' autoport='yes'
listen='127.0.0.1' passwd='123'>
    </graphics>

    # cat change-passwd.xml
    <graphics type='vnc' port='-1' autoport='yes' 
listen='127.0.0.1' passwd=''/>
    # virsh update-device dom2 change-passwd.xml

    # virsh dumpxml dom2 --security-info |grep graphics
    <graphics type='vnc' port='5900' autoport='yes'
listen='127.0.0.1' passwd=''>
    </graphics>

    login the guest with virt-viewer command
    # virt-viewer testks
    also can connect the guest dom2 success with empty password

4. I produce the same steps on RHEL6.6 libvirt-0.10.2-46.el6.x86_64, the guest
can not be connected when set graphics vnc password to empty, the same result
with bug 859317.

Actual results:
we can login the guest when set the graphics passwd empty

Expected results:
I am not sure what is the right behaviour for RHEL7?

thank