Merge branch 'catlee/empty_parallel' into 'master'

Exit from run early if we have no handlers

Closes #226

See merge request os85/httpx!239

lib/httpx/adapters/faraday.rb

@@ -169,6 +169,8 @@ module Faraday
         end
 
         def run
+          return unless @handlers.last
+
           env = @handlers.last.env
 
           session = HTTPX.session.with(options_from_env(env))

test/adapters/faraday_test.rb

@@ -45,6 +45,11 @@ class FaradayTest < Minitest::Test
     refute_nil resp1.env[:error]
   end
 
+  def test_adapter_in_parallel_no_requests
+    connection = create_connection
+    assert_nil(connection.in_parallel {})
+  end
+
   def test_adapter_get_handles_compression
     res = get(build_path("/gzip"))
     assert JSON.parse(res.body.to_s)["gzipped"]