Consider the following code:

    public static Mono<String> myFunction(boolean condition) {
        if (condition) {
            // returns Mono<String>
            return Mono.fromSupplier(() -> "Hello, World!"); 
        } else {
            // returns Mono<Void>  
            return Mono.fromRunnable(() -> System.out.println("Running a task...")); 
        }
    }

This code compiles and run perfectly fine. Mono.fromSupplier returns String, whereas Mono.fromRunnable returns Mono<Void>, then ideally compilation should fail. What am I missing?