Changing a build definition with the Java API

Hi. I'm writing a program to change a build definition trying to change a build def property (buildforge to jenkins).
Can anyone help with the error message (state id and item id)
Thanks.
regards
Sola

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buildClient = (ITeamBuildClient) this.teamRepository.getClientLibrary(ITeamBuildClient.class);

IBuildDefinition bd = buildClient.getBuildDefinition(bdName, rtc.getMonitor());
IBuildDefinition wc = (IBuildDefinition) bd.getWorkingCopy();
wc.setProperty("com.ibm.team.build.internal.template.id", "com.ibm.rational.connector.hudson.ui.buildDefinitionTemplate");
bd = buildClient.getBuildClient().save(bd, rtc.getMonitor());

throwing an exception for some missing values:

java.lang.IllegalArgumentException: Item id and State id must not be null
    at com.ibm.team.repository.service.internal.RepositoryItemService.fetchState(RepositoryItemService.java:695)
    at sun.reflect.GeneratedMethodAccessor430.invoke(null)