For this bug to be triggered, it takes an intercepted class with a producer field in it. See attached maven project as a very small code base for this. It runs directly as JavaSE (Main#main) for your convenience.
org.apache.webbeans.portable.ProducerFieldProducer will eventually access the field inside the generated OwbInterceptProxy instead of the actual bean. This means that "null" values are produced, not the actual values generated in the intercepted class.
Affected line as of 1.6.2 is 84: instance = (T) field.get(parentInstance)
parentInstance is a proxy object, not the actual bean. Therefore instance will be null.