Spring NullPointerException in BindingReflectionHintsRegistrar for anonymous classes

The shouldSkipMembers method uses type.getCanonicalName(), which may return null for anonymous, local and other types leading to NPE when calling startsWith.

The above happened when reading Java8 compiled code of com.mongodb.connection.ServerType. Retrieving constructor arguments and registering them for binding failed because a synthetic constructor uses an anonymous class (com.mongodb.connection.ServerType$1).

synthetic ServerType(java.lang.String arg0, int arg1, com.mongodb.connection.ServerType$1 arg2) { // <init> //(Ljava/lang/String;ILcom/mongodb/connection/ServerType$1;)V
    <localVar:index=0 , name=this , desc=Lcom/mongodb/connection/ServerType;, sig=null, start=L0, end=L1>
    <localVar:index=1 , name=x0 , desc=Ljava/lang/String;, sig=null, start=L0, end=L1>
    <localVar:index=2 , name=x1 , desc=I, sig=null, start=L0, end=L1>
    <localVar:index=3 , name=x2 , desc=Lcom/mongodb/connection/ServerType$1;, sig=null, start=L0, end=L1>

    L0 {
        aload 0 // reference to self
        aload 1 // reference to arg0
        iload 2 // reference to arg1
        invokespecial com/mongodb/connection/ServerType.<init>(Ljava/lang/String;I)V
        return
    }
    L1 {
    }
}

ReflectionHints hints = new ReflectionHints();
BindingReflectionHintsRegistrar reflectionHintsRegistrar = new BindingReflectionHintsRegistrar();
Arrays.stream(com.mongodb.connection.ServerType.class.getDeclaredConstructors()).forEach(ctor -> {
    Arrays.stream(ctor.getParameterTypes()).forEach(type -> {
        reflectionHintsRegistrar.registerReflectionHints(hints, type);
    });
});

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "String.startsWith(String)" because the return value of "java.lang.Class.getCanonicalName()" is null
    at org.springframework.aot.hint.BindingReflectionHintsRegistrar.shouldSkipMembers(BindingReflectionHintsRegistrar.java:74)
    at org.springframework.aot.hint.BindingReflectionHintsRegistrar.lambda$registerReflectionHints$0(BindingReflectionHintsRegistrar.java:87)
    at org.springframework.aot.hint.ReflectionHints.registerType(ReflectionHints.java:86)
    at org.springframework.aot.hint.ReflectionHints.registerType(ReflectionHints.java:109)
    at org.springframework.aot.hint.BindingReflectionHintsRegistrar.registerReflectionHints(BindingReflectionHintsRegistrar.java:86)
    at org.springframework.aot.hint.BindingReflectionHintsRegistrar.registerReflectionHints(BindingReflectionHintsRegistrar.java:65)

related: spring-projects/spring-data-mongodb#4248

Comment From: bclozel

Thanks @christophstrobl for the analysis!