Pattern Guards fooled by null

A sadness:

Pattern guards don't handle nulls well, and, also, introducing a pattern guard appears to make a default _ not match on null values:

scala> def guard_fails(s: String) {
| s match {
| case s: String if s == null => println("null")
| case s: String if s != null => println("s=" + s)
| case _ => println("default")
| }
| }
guard_fails: (String)Unit

scala> guard_fails("test")
s=test

scala> guard_fails(null)
scala.MatchError
at .guard_fails(:5)
at .(:6)
at .()
at RequestResult$.(:3)
at RequestResult$.()
at RequestResult$result()
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMeth...
scala>

scala> def guard_fails2(s: String) {
| s match {
| case s: String if s != null => println("s=" + s)
| case _ => println("default")
| }
| }
guard_fails2: (String)Unit

scala> guard_fails2("test")
s=test

scala> guard_fails2(null)
scala.MatchError
at .guard_fails2(:5)
at .(:6)
at .()
at RequestResult$.(:3)
at RequestResult$.()
at RequestResult$result()
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMet...
scala>

To code this match defensively, you have to define a null pattern explicitly:

scala> def ok(s: String) {
| s match {
| case s: String if true => println("s=" + s)
| case null => println("null")
| case _ => println("default")
| }
| }
ok: (String)Unit

scala> ok("test")
s=test

scala> ok(null)
null

scala>