This class:

public primitive class CheckRefLambda.val {
    int theInteger;
    public CheckRefLambda(int newValue) {
        theInteger = newValue;
    }
    public Supplier<CheckRefLambda.ref> makeCopier() {
        return () -> new CheckRefLambda(this.theInteger + 1);
    }
    // ...
}

won't bootstrap the lambda, but fails with:

java.lang.BootstrapMethodError: bootstrap method initialization exception
at java.base/java.lang.invoke.BootstrapMethodInvoker.invoke(BootstrapMethodInvoker.java:188)
at java.base/java.lang.invoke.CallSite.makeSite(CallSite.java:315)
at java.base/java.lang.invoke.MethodHandleNatives.linkCallSiteImpl(MethodHandleNatives.java:281)
at java.base/java.lang.invoke.MethodHandleNatives.linkCallSite(MethodHandleNatives.java:271)
at CheckRefLambda.makeCopyer(CheckRefLambda.java:42)
at CheckRefLambda.main(CheckRefLambda.java:47)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:569)
at com.sun.javatest.regtest.agent.MainActionHelper$AgentVMRunnable.run(MainActionHelper.java:312)
at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: java.lang.invoke.LambdaConversionException: Invalid receiver type primitive CheckRefLambda; not a subtype of implementation type primitive CheckRefLambda
at java.base/java.lang.invoke.AbstractValidatingLambdaMetafactory.validateMetafactoryArgs(AbstractValidatingLambdaMetafactory.java:271)
at java.base/java.lang.invoke.LambdaMetafactory.metafactory(LambdaMetafactory.java:340)
at java.base/java.lang.invoke.BootstrapMethodInvoker.invoke(BootstrapMethodInvoker.java:134)
... 11 more