Application is deployed to context "/" in Wildfly.

In "undertow-servlet-1.0.15.Final.jar"
in method
ServletContainerImpl->addDeployment
in row

deploymentsByPath.put(dep.getContextPath(), deploymentManager);

dep.getContextPath() returns the string ""
and method
ServletContainerImpl->getDeploymentByPath
in row

return deploymentsByPath.get("");

returns our deployment.

In "undertow-servlet-1.1.0.Final.jar"
in method
ServletContainerImpl->addDeployment
in row

deploymentsByPath.put(dep.getContextPath(), deploymentManager);

dep.getContextPath() returns the string "/"
and method
ServletContainerImpl->getDeploymentByPath
in row

return deploymentsByPath.get("");

returns NULL.

So it's impossible to get deployment with root context.
Change to

return deploymentsByPath.get("/");

will fix this.