Ant OK, mas ocorre erro no build do projeto Leiloes

Estou com o Ant instalado e respondendo no prompt de comando do Windows 10. Porém, ainda enfrento erro no build do projeto Leiloes. O ambiente http://localhost:8080 apresenta:

HTTP ERROR: 503
SERVICE_UNAVAILABLE
RequestURI=/

Na janela do CMD do windows, é possível verificar os erros abaixo:

[ivy:retrieve]  0 artifacts copied, 65 already retrieved (0kB/68ms)
     [copy] Copying 46 files to C:\Users\_win_user_\leiloes\src\main\webapp\WEB-INF\lib

compile:
    [javac] C:\Users\_win_user_\leiloes\build.xml:41: warning: 'includeantruntime' was not set, defaulting to build.sysclasspath=last; set to false for repeatable builds
    [javac] Compiling 15 source files to C:\Users\_win_user_\leiloes\src\main\webapp\WEB-INF\classes
     [copy] Copying 4 files to C:\Users\_win_user_\leiloes\src\main\webapp\WEB-INF\classes

jetty.run:
    [jetty] Configuring Jetty for project: vraptor-scaffold
    [jetty] 2019-01-02 13:38:38.964::INFO:  Logging to STDERR via org.mortbay.log.StdErrLog
    [jetty]
    [jetty] Configuring Jetty for web application: leiloes
    [jetty] Webapp source directory = C:\Users\_win_user_\leiloes\src\main\webapp
    [jetty] Context path = /
    [jetty] Classpath = []
    [jetty] Default scanned paths = []
    [jetty] Extra scan targets = [C:\Users\_win_user_\leiloes\src\main\webapp\WEB-INF\classes]
    [jetty] Temp directory = C:\Users\_win_user_\leiloes\target\jetty-temp\
    [jetty] web.xml file = C:\Users\_win_user_\leiloes\src\main\webapp\WEB-INF\web.xml
    [jetty] 2019-01-02 13:38:39.277::INFO:  jetty-6.1.14
    [jetty] 2019-01-02 13:38:39.677::INFO:  org.mortbay.jetty.ant.JettyWebAppConfiguration does not support annotations on source. Use org.mortbay.jetty.annotations.Configuration instead
    [jetty] 2019-01-02 13:38:39.686::INFO:  No Transaction manager found - if your webapp requires one, please configure one.
    [jetty] 19-01-02 13:38:40,287 [INFO] br.com.caelum.vraptor.config.BasicConfiguration - Using class br.com.caelum.vraptor.ioc.spring.SpringProvider as Container Provider
    [jetty] 19-01-02 13:38:40,334 [INFO] br.com.caelum.vraptor.ioc.spring.DefaultSpringLocator - No application context found
    [jetty] 19-01-02 13:38:40,433 [INFO] br.com.caelum.vraptor.scan.WebAppBootstrapFactory - No static WebAppBootstrap found.
    [jetty] 19-01-02 13:38:40,441 [INFO] br.com.caelum.vraptor.config.BasicConfiguration - br.com.caelum.vraptor.scanning = null
    [jetty] 2019-01-02 13:38:40.556::WARN:  failed vraptor
    [jetty] br.com.caelum.vraptor.scan.ScannerException: Could not scan WEB-INF/classes
    [jetty]     at br.com.caelum.vraptor.scan.ScannotationComponentScanner.scanWebInfClasses(ScannotationComponentScanner.java:74)
    [jetty]     at br.com.caelum.vraptor.VRaptor.init(VRaptor.java:103)
    [jetty]     at org.mortbay.jetty.servlet.FilterHolder.doStart(FilterHolder.java:97)
    [jetty]     at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:292)
    [jetty]     at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    [jetty]     at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    [jetty]     at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:99)
    [jetty]     at org.apache.tools.ant.launch.Launcher.main(Launcher.java:101)
    [jetty] Caused by: java.io.IOException: invalid constant type: 18
    [jetty]     at javassist.bytecode.ConstPool.readOne(ConstPool.java:1027)
    [jetty]     at org.scannotation.AnnotationDB.scanClass(AnnotationDB.java:311)
    [jetty]     at br.com.caelum.vraptor.scan.ScannotationComponentScanner.scanWebInfClasses(ScannotationComponentScanner.java:71)
    [jetty]     ... 40 more
    [jetty] 2019-01-02 13:38:40.625::WARN:  Failed startup of context org.mortbay.jetty.webapp.WebAppContext@69a2b3b6{/,C:\Users\_win_user_\leiloes\src\main\webapp}
    [jetty] br.com.caelum.vraptor.scan.ScannerException: Could not scan WEB-INF/classes
    [jetty]     at br.com.caelum.vraptor.scan.ScannotationComponentScanner.scanWebInfClasses(ScannotationComponentScanner.java:74)
    [jetty]     at org.mortbay.jetty.servlet.FilterHolder.doStart(FilterHolder.java:97)
    [jetty]     at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:460)
    [jetty]     at org.apache.tools.ant.launch.Launcher.main(Launcher.java:101)
    [jetty] Caused by: java.io.IOException: invalid constant type: 18
    [jetty]     at javassist.bytecode.ConstPool.readOne(ConstPool.java:1027)
    [jetty]     at org.scannotation.AnnotationDB.scanClass(AnnotationDB.java:311)
    [jetty]     at br.com.caelum.vraptor.scan.ScannotationComponentScanner.scanWebInfClasses(ScannotationComponentScanner.java:71)
    [jetty]     ... 40 more
    [jetty] 2019-01-02 13:38:40.876::INFO:  Started SelectChannelConnector@0.0.0.0:8080
    [jetty] Web application 'leiloes': starting scanner at interval of 3 seconds.