It's inconvenient because null could be considered a case

  switch(s) {
    case null: return false;
    case "y": return true;
    default: return false;
  }

The broader issue is that Java handles null inconveniently.

1) Every object can be null, switch requires the argument to be non-null, and the type system doesn't warn you when NPE are possible. A type system which handles nullability could fail to compile if 's' is nullable. Kotlin does this, and it let's you opt-in to the NPE with some convenient syntax:

  switch(s!!)

2) It's inconvenient to handle null as a value. To properly handle the null case without throwing, you need to do one the following:

  if(s == null) { ... }
  else switch(s) { ... }

  switch(s == null ? "some-default" : s)

The first way can be made more convenient if you change switch to work on nullable values. The second way is inconvenient, so people generally skip it. If you want switch to only work on non-null values, there're more convenient syntaxes to handle null, such as the 'elvis operator':

  switch(s ?: "some-default")