If you compare the costs of implicit null checks vs explicit checks, like this:

    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    public int do_Implicit(MyObject o) {
        return o.x;
    }

    @CompilerControl(CompilerControl.Mode.DONT_INLINE)
    public int do_Explicit(MyObject o) {
        if (o == null) {
            throw new NullPointerException("Boo");
        }
        return o.x;
    }

Then you will notice the implicit null checks are 4-5x more costly:
  testExplicit: 1551.416 ± 67.577 us/op
  testImplicit: 8177.205 ± 631.399 us/op

Profiling testImplicit yields:

Call Tree: FUNCTIONS. Complete view. Threshold: 1% Sort by: metric. Metric: Attributed Total CPU Time
+- 11.058 (100%) <Total>
  +- 6.304 (57%) RuntimeStub - throw_null_pointer_exception Runtime1 stub
  | +- 6.264 (57%) Runtime1::throw_null_pointer_exception(JavaThread*)
  | +- 3.863 (35%) SharedRuntime::throw_and_post_jvmti_exception(JavaThread*,Handle)
  | | +- 3.843 (35%) Exceptions::_throw(Thread*,const char*,int,Handle,const char*)
  | | +- 3.032 (27%) oopDesc::print_value_string()
  | | | +- 3.022 (27%) InstanceKlass::oop_print_value_on(oopDesc*,outputStream*)
  | | | +- 2.942 (27%) Symbol::print_value_on(outputStream*)const
  | | | | +- 2.912 (26%) outputStream::print(const char*,...)
  | | | | +- 2.212 (20%) outputStream::do_vsnprintf(char*,unsigned long,const char*,__va_list_tag*,bool,unsigned long&)
  | | | | | +- 1.861 (17%) vsnprintf
  | | | | | | +- 1.131 (10%) vfprintf
  | | | | | | | +- 0.150 (1%) _IO_default_xsputn
  | | | | | | | +- 0.080 (1%) strchrnul

This happens because the log message is constructed always, regardless of LogEvents setting that is allegedly supposed to filter these:

void Exceptions::_throw(Thread* thread, const char* file, int line, Handle h_exception, const char* message) {
 ...
  // vm log
  Events::log_exception(thread, "Exception <%s%s%s> (" INTPTR_FORMAT ") thrown at [%s, line %d]",
                        h_exception->print_value_string(), message ? ": " : "", message ? message : "",
                        (address)h_exception(), file, line);
}

inline void Events::log_exception(Thread* thread, const char* format, ...) {
  if (LogEvents) {
    va_list ap;
    va_start(ap, format);
    _exceptions->logv(thread, format, ap);
    va_end(ap);
  }
}

Notice "print_value_string" call in the "log_exception" arguments.