Seam Builder rises NullPointerException during build if model is not set up on project for some reason.
See the stacktrace below:

Contains: Errors running builder 'Seam Builder' on project 'seam_war-test'.
java.lang.NullPointerException
at org.jboss.tools.common.model.filesystems.FileSystemsHelper.getFileSystems(FileSystemsHelper.java:21)
at org.jboss.tools.common.model.filesystems.FileSystemsHelper.getLibs(FileSystemsHelper.java:37)
at org.jboss.tools.common.model.project.ext.AbstractClassPathMonitor.update(AbstractClassPathMonitor.java:59)
at org.jboss.tools.seam.internal.core.scanner.lib.ClassPath.build(ClassPath.java:177)
at org.jboss.tools.seam.internal.core.SeamProject.build(SeamProject.java:372)
at org.jboss.tools.seam.core.SeamCoreBuilder.build(SeamCoreBuilder.java:50)
at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:717)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:191)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:228)
at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:281)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:284)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:245)
at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:383)
at org.eclipse.core.internal.resources.Project$1.run(Project.java:618)
at org.eclipse.core.internal.resources.Workspace.run(Workspace.java:2310)
at org.eclipse.core.internal.resources.Project.internalBuild(Project.java:597)
at org.eclipse.core.internal.resources.Project.build(Project.java:114)
at org.jboss.tools.test.util.ProjectImportTestSetup.loadProject(ProjectImportTestSetup.java:67)
at org.jboss.tools.seam.ui.test.wizard.Seam12WARNewOperationTest.setUp(Seam12WARNewOperationTest.java:67)
at org.jboss.tools.seam.ui.test.wizard.Seam20WARNewOperationTest.setUp(Seam20WARNewOperationTest.java:50)