Fix NPE in PagedSeq.slice at end of seq

See https://github.com/scala/scala-parser-combinators/issues/70

Basically the same thing as SI-6615, including the fact everything
works okay if the PagedSeq is printed before calling slice.

It might seem strange that this allows taking slices that start beyond
the end, but
 - this was possible anyway if one forced the entire sequence, and
 - it is reasonable to be able to take a slice at the very end (not
   beyond it) and get an empty sequence, which is exactly what
   StreamReader in scala-parser-combinators does and gets an NPE.

1 files changed, 6 insertions, 0 deletions

diff --git a/test/junit/scala/collection/immutable/PagedSeqTest.scala b/test/junit/scala/collection/immutable/PagedSeqTest.scala
index 2b576a3655..74f8825307 100644
--- a/test/junit/scala/collection/immutable/PagedSeqTest.scala
+++ b/test/junit/scala/collection/immutable/PagedSeqTest.scala
@@ -13,6 +13,12 @@ class PagedSeqTest {
     assertEquals(Seq('a'), PagedSeq.fromStrings(List.fill(5000)("a")).slice(4096, 4097))
   }
 
+  // should not NPE, and should be empty
+  @Test
+  def test_SI9480(): Unit = {
+    assertEquals(Seq(), PagedSeq.fromStrings(List("a")).slice(1))
+  }
+
   // Slices shouldn't read outside where they belong
   @Test
   def test_SI6519 {