Invalid EL expressions should generate a Failure with a proper explanation rather than this stack trace:

Caused by: javax.el.ELException: Function 's:hasPermission' not found
at org.jboss.el.lang.ExpressionBuilder.visit(ExpressionBuilder.java:187)
at org.jboss.el.parser.SimpleNode.accept(SimpleNode.java:129)
at org.jboss.el.lang.ExpressionBuilder.prepare(ExpressionBuilder.java:138)
at org.jboss.el.lang.ExpressionBuilder.build(ExpressionBuilder.java:152)
at org.jboss.el.lang.ExpressionBuilder.createValueExpression(ExpressionBuilder.java:206)
at org.jboss.el.ExpressionFactoryImpl.createValueExpression(ExpressionFactoryImpl.java:68)
at org.jboss.resteasy.links.impl.EL.evaluateBoolean(EL.java:67)
at org.jboss.resteasy.links.impl.RESTUtils.checkConstraint(RESTUtils.java:171)
at org.jboss.resteasy.links.impl.RESTUtils.processLinkResource(RESTUtils.java:131)
at org.jboss.resteasy.links.impl.RESTUtils.processLinkResources(RESTUtils.java:113)
at org.jboss.resteasy.links.impl.RESTUtils.addDiscovery(RESTUtils.java:56)
at org.jboss.resteasy.links.impl.LinkDecorator$1.beforeMarshal(LinkDecorator.java:27)
at com.sun.xml.internal.bind.v2.runtime.XMLSerializer.fireBeforeMarshalEvents(XMLSerializer.java:740)
at com.sun.xml.internal.bind.v2.runtime.XMLSerializer.childAsRoot(XMLSerializer.java:479)
at com.sun.xml.internal.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:314)
at com.sun.xml.internal.bind.v2.runtime.MarshallerImpl.marshal(MarshallerImpl.java:243)
at javax.xml.bind.helpers.AbstractMarshallerImpl.marshal(AbstractMarshallerImpl.java:75)
at org.jboss.resteasy.plugins.providers.jaxb.AbstractJAXBProvider.writeTo(AbstractJAXBProvider.java:105)
at org.jboss.resteasy.core.interception.MessageBodyWriterContextImpl.proceed(MessageBodyWriterContextImpl.java:117)