Fix a bug in do-block tree normalization

src/chisels.jl

@@ -154,7 +154,9 @@ function normalize_tree!(node)
             # If the tuple ends with a K"NewlineWs" node we move it into the block
             block = kids[blockidx]
             blockkids = verified_kids(block)
+            if length(blockkids) > 0
                 @assert kind(blockkids[1]) !== K"Whitespace"
+            end
             pushfirst!(blockkids, pop!(tuplekids))
             # Remake the nodes to recompute the spans
             kids[tupleidx] = make_node(tuple, tuplekids)

test/runtests.jl

@@ -1033,6 +1033,7 @@ end
         end
         # do-end
         @test format_string("open() do\na$(d)end") == "open() do\n    a\nend"
+        @test format_string("open() do\nend") == "open() do\nend"
         @test_broken format_string("open() do;a$(d)end") == "open() do\n    a\nend"
         @test_broken format_string("open() do ;a$(d)end") == "open() do\n    a\nend"
         @test format_string("open() do io$(d)a end") == "open() do io\n    a\nend"