integer_at should return nil for empty integer captures

lib/strscan/strscan.rb

@@ -3,7 +3,8 @@
 class StringScanner
   unless method_defined?(:integer_at) # For JRuby
     def integer_at(specifier, *to_i_args)
-      self[specifier]&.to_i(*to_i_args)
+      value = self[specifier]
+      value.to_i(*to_i_args) unless value.nil? || value.empty?
     end
   end
 

lib/strscan/truffleruby.rb

@@ -133,7 +133,15 @@ def [](group)
     end
   end
 
-  def integer_at(group, *to_i_args) = self[group]&.to_i(*to_i_args)
+  def integer_at(group, *to_i_args)
+    return if self[group].nil?
+
+    group += @last_match.size if Primitive.is_a?(group, Integer) && group < 0
+    from = @last_match.bytebegin(group)
+    to = [@last_match.byteend(group), @string.bytesize].min
+    value = @string.byteslice(from, to - from)
+    value.to_i(*to_i_args) unless value.nil? || value.empty?
+  end
 
   def values_at(*groups) = @last_match&.values_at(*groups)
 

test/strscan/test_stringscanner.rb

@@ -578,9 +578,14 @@ def test_integer_at_base_auto
     assert_integer_at(s, 0, 0) # 0xaf
   end
 
-  def test_integer_at_shrunk
-    omit("not supported on TruffleRuby") if RUBY_ENGINE == "truffleruby"
+  def test_integer_at_empty
+    s = create_string_scanner("")
+    assert_equal("", s.scan(/()/))
+    assert_nil(s.integer_at(0))
+    assert_nil(s.integer_at(1))
+  end
 
+  def test_integer_at_shrunk
     s = create_string_scanner(+"before 29 after")
     s.skip_until(" ")
     assert_equal("29", s.scan(/\d+/))
@@ -589,8 +594,6 @@ def test_integer_at_shrunk
   end
 
   def test_integer_at_shrunk_partial
-    omit("not supported on TruffleRuby") if RUBY_ENGINE == "truffleruby"
-
     s = create_string_scanner(+"before 29 after")
     s.skip_until(" ")
     assert_equal("29", s.scan(/\d+/))