Updated the issue formatting to make it easier to read.
Corrected minor textual errors.

The escaping that was added was indended to apply to build parameters (values here expected to be literal), NOT properties entered directly into the ant build step (variable expansion supported here).. will need to dig into how to handle these separately.

out of curiosity, what if you enter just
value=
in the properties? Does that work for empty value?

I found that the person reporting a similar problem on the alias was using %VAR% form instead of $VAR.. even running ant build on windows you should use $VAR form in the ant properties box, as Hudson will expand that before any escaping is done.
So, if just
value=
works for the case you're reporting here, then I'm inclined to close this issue. Let me know how it goes, and if you know of any other cases that don't work with the new escaping stuff. Thanks.

Defining a property without a value makes the Hudson build fail. If the test is run directly against Ant from a command prompt Ant reports: "Missing value for property value".

Steps:
1) Change the Ant properties to:

value=

Hudson console output:

Started by user anonymous
Building on master
[workspace] $ cmd.exe /C '"ant.bat -Dvalue= && exit %%ERRORLEVEL%%"'
Unable to locate tools.jar. Expected to find it in C:\Program Files\Java\jre6\lib\tools.jar
Missing value for property value
Finished: FAILURE

Single quotes seems to escaped correctly in Hudson. Ant reports the same value in Hudson as when the the script is run from a command prompt.

Hudson console output on single quotes:

Started by user anonymous
Building on master
[workspace] $ cmd.exe /C '"ant.bat -Dvalue='' && exit %%ERRORLEVEL%%"'
Unable to locate tools.jar. Expected to find it in C:\Program Files\Java\jre6\lib\tools.jar
Buildfile: build.xml

build:
     [echo] Value: ''''

BUILD SUCCESSFUL
Total time: 0 seconds
Finished: SUCCESS

yes, I see that too.. that's odd.
"ant -Dfoo= mytest" works fine on unix..
I'll see what I can do..

Code changed in hudson
User: : mindless
Path:
trunk/hudson/main/core/src/main/java/hudson/tasks/Ant.java
trunk/hudson/main/core/src/main/java/hudson/util/ArgumentListBuilder.java
trunk/hudson/main/war/resources/help/ant/ant-properties.html
http://jenkins-ci.org/commit/33988
Log:
JENKINS-7204 fix for defining empty properties for ant build on windows.
also added info about parameter references and double quotes in help file.

Please test with http://ci.hudson-labs.org/job/hudson_main_trunk/lastSuccessfulBuild/artifact/main/war/target/hudson.war and let me know if it works.. you should use
name=
instead of
name=""

Integrated in hudson_main_trunk #196
JENKINS-7204 fix for defining empty properties for ant build on windows.
also added info about parameter references and double quotes in help file.

mindless :
Files :

• /trunk/hudson/main/war/resources/help/ant/ant-properties.html
• /trunk/hudson/main/core/src/main/java/hudson/tasks/Ant.java
• /trunk/hudson/main/core/src/main/java/hudson/util/ArgumentListBuilder.java

Tested the hudson_main_trunk #196 build. It works perfectly.

Setting value to:

value=""

Gives the output:

[workspace] $ cmd.exe /C '"ant.bat "-Dvalue=""""" && exit %%ERRORLEVEL%%"'
Buildfile: build.xml

build:
     [echo] Value: '""'
BUILD SUCCESSFUL

Setting value to:

value=

Gives the output:

[workspace] $ cmd.exe /C '"ant.bat -Dvalue="" && exit %%ERRORLEVEL%%"'
Buildfile: build.xml

build:
     [echo] Value: ''

BUILD SUCCESSFUL

Setting value to:

value=''

Gives the output:

[workspace] $ cmd.exe /C '"ant.bat -Dvalue='' && exit %%ERRORLEVEL%%"'
Buildfile: build.xml

build:
     [echo] Value: ''''

BUILD SUCCESSFUL

This is not quite working for all parameters. I am using parameters in the job configuration, set as follows:

[Choice] environment=sys-test
[String] releaseTag=September_2010.9708
[String] dbVersion=September_2010
[String] dbOrigin=
[String] comments=
[String] datetime=
[Choice] tester=

This results in $ cmd.exe /C '"ant.bat -file build-trac.xml -Dtester="" -DdbOrigin= -DreleaseTag=September_2010.9708 -Denvironment=sys-test -Ddatetime="" -Dcomments= -DdbVersion=September_2010 -DdeployEnvironment=ci updateDeploymentHistory -verbose && exit %%ERRORLEVEL%%"'

which fails because of the lack of quotes on dbOrigin and comments. I don't understand why these are treated differently from datetime, which is quoted correctly and works.

I am using Windows XP SP3 for client and server, Hudson 1.374

Another problem with Ant command line quoting - comma in a property value:
name=foo,bar

Code changed in hudson
User: : mindless
Path:
trunk/hudson/main/core/src/main/java/hudson/tasks/Ant.java
trunk/www/changelog.html
http://jenkins-ci.org/commit/34228
Log:
JENKINS-7204 update regexp to work for 2 consecutive empty properties

Integrated in hudson_main_trunk #234
JENKINS-7204 update regexp to work for 2 consecutive empty properties

mindless :
Files :

• /trunk/www/changelog.html
• /trunk/hudson/main/core/src/main/java/hudson/tasks/Ant.java