Camel will use JNDI as the default Registry implementation if you do not use Spring. This means that using a DefaultCamelContext will try and create a JndiRegistry which uses the JNDI InitialContext as the registry.
This means you need to configure some JNDI provider to be able to use this. This is described in this FAQ entry, but essentially you just need to create a file called jndi.properties on the classpath and configure it with the JNDI provider you wish.
You can use the Camel JNDI provider by using the following jndi.properties file