Check for nil host before match?.

lib/http/request.rb

@@ -326,11 +326,9 @@ def port
     # @return [String]
     # @api private
     def default_host_header_value
-      value = PORTS[@scheme] == port ? host : "#{host}:#{port}"
+      raise RequestError, "Invalid host: #{host.inspect}" if host.nil? || host.match?(/\s/)
 
-      raise RequestError, "Invalid host: #{value.inspect}" if value.match?(/\s/)
-
-      value
+      PORTS[@scheme] == port ? host : "#{host}:#{port}"
     end
 
     # Parse and normalize the URI, setting scheme

test/http/request_test.rb

@@ -266,6 +266,18 @@ def test_host_header_when_host_contains_whitespace_includes_invalid_host_in_erro
     assert_includes err.message, "exam ple.com".inspect
   end
 
+  def test_host_header_when_host_is_nil_raises_request_error
+    normalizer = lambda { |uri|
+      u = HTTP::URI.parse(uri)
+      u.host = nil
+      u
+    }
+
+    assert_raises(HTTP::RequestError) do
+      HTTP::Request.new(verb: :get, uri: "http://example.com/", uri_normalizer: normalizer)
+    end
+  end
+
   # User-Agent header
 
   def test_user_agent_header_defaults_to_http_request_user_agent