Return nil for empty integer captures

JRuby must match the native implementation when captures become empty.

Author: nobu

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
 

test/strscan/test_stringscanner.rb

@@ -578,6 +578,13 @@ def test_integer_at_base_auto
     assert_integer_at(s, 0, 0) # 0xaf
   end
 
+  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
     omit("not supported on TruffleRuby") if RUBY_ENGINE == "truffleruby"