Bitbucket uses system default version of Java even if it is unsupported

Exception in thread "main" java.lang.NoClassDefFoundError: java/util/Base64

Likely root cause: java.lang.ClassNotFoundException: java.util.Base64
 at java.net.URLClassLoader$1.run(URLClassLoader.java:359)
 at java.net.URLClassLoader$1.run(URLClassLoader.java:348)
 at java.security.AccessController.doPrivileged(Native Method)
 at java.net.URLClassLoader.findClass(URLClassLoader.java:347)
 at java.lang.ClassLoader.loadClass(ClassLoader.java:425)
 at java.net.FactoryURLClassLoader.loadClass(URLClassLoader.java:786)
 at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
 at com.atlassian.elasticsearch.buckler.BasicAuth.encodeCredentials(BasicAuth.java:22)
 at com.atlassian.elasticsearch.buckler.config.AuthConfig.<init>(AuthConfig.java:25)
 at com.atlassian.elasticsearch.buckler.config.BucklerConfig.<init>(BucklerConfig.java:55)
 at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
 at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
 at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
 at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
 at <<<guice>>>
 at org.elasticsearch.node.Node.<init>(Node.java:213)
 at org.elasticsearch.node.Node.<init>(Node.java:140)
 at org.elasticsearch.node.NodeBuilder.build(NodeBuilder.java:143)
 at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:178)
 at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:270)
 at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:35)