Glassfish/Wildfly not failing if @Resource cannot be resolved?

I am experimenting with @Resource in a servlet to see if we can use it to inject configuration parameters easily (this is servlet 3.0 webapp in Glassfish 4.1.1).

I was told in https://stackoverflow.com/a/45715196/53897 that the behavior I saw of a @Resource String userName being null when used if it could not be resolved if the env-entries in web.xml were not present, to be wrong according to the specification, but that the behavior of WildFly was the same.

Question is: Is this a known bug? Is there a flag that can enforce the "fail if not resolvable"?

This is allowed for simple env entries:

EE.5.4.1.3

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It’s often convenient to declare a field or method as an injection target, but specify a default value in the code, as illustrated in the following example.

// The maximum number of tax exemptions, configured by the Deployer.
@Resource int maxExemptions = 4; // defaults to 4

To support this case, the container must only inject a value for this resource if the deployer has specified a value to override the default value.
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