The latest Hudson seems to quote Ant properties incorrectly. Older versions of Hudson did not have the same problem. The quote problem makes it impossible to define an empty Ant property.

Steps to reproduce:

1. Create new free style job
2. Run the job to create a workspace folder
3. Add the following file to the job workspace:
   build.xml

   <project default="build" basedir=".">
       <target name="build">
           <echo message="Value: '${value}'" />
       </target>
   </project>
   

4. Reconfigure the hudson job to invoke Ant
5. In the Ant properties field write:

   value=""
   

6. Run the job
   
   

Excepted result:
The Ant script should show that the value property was blank

Actual result:
The Ant script show that the value property is actual "".

Additional information:
In the console output of the job Hudson 1.371 displays:
[workspace] $ cmd.exe /C '"ant.bat "-Dvalue=""""" && exit %%ERRORLEVEL%%"'

In the console output of the job in older Hudson's (1.361 and earlier) displayed:
[workspace] $ cmd.exe /C '"ant.bat -Dvalue="" build && exit %%ERRORLEVEL%%"'