abrt 1.0.3 detected a crash.

How to reproduce
-----
1.display conversion for liguid volume conversion.
2.leave app running unattended for 20 minutes
3.return and attempted to close the app with the close window icon in the upper right corner.  


backtrace
-----
Summary: TB7bdfd1c6 gonvert:538:top:ValueError: invalid literal for float(): .

Traceback (most recent call last):
  File "/usr/bin/gonvert", line 538, in top
    value = float(entry2.get_text())
ValueError: invalid literal for float(): .

Local variables in innermost frame:
a: <gtk.Entry object at 0xb737f0a4 (GtkEntry at 0x9fb7908)>
self: <__main__.Ccalculate instance at 0xb737cbcc>

cmdline: /usr/bin/python /usr/bin/gonvert
component: gonvert
executable: /usr/bin/gonvert
kernel: 2.6.31.12-174.2.3.fc12.i686
package: gonvert-0.2.20-2.fc12
uuid: 7bdfd1c6