diff --git a/lib/rspec_api_documentation/curl.rb b/lib/rspec_api_documentation/curl.rb
index 31a2b1d8..4e6bc174 100644
--- a/lib/rspec_api_documentation/curl.rb
+++ b/lib/rspec_api_documentation/curl.rb
@@ -69,7 +69,7 @@ def format_header(header)
     end
 
     def format_full_header(header, value)
-      formatted_value = value.gsub(/"/, "\\\"")
+      formatted_value = value ? value.gsub(/"/, "\\\"") : ''
       "#{format_header(header)}: #{formatted_value}"
     end
 
diff --git a/spec/curl_spec.rb b/spec/curl_spec.rb
index 275a60c1..180b79ec 100644
--- a/spec/curl_spec.rb
+++ b/spec/curl_spec.rb
@@ -15,7 +15,8 @@
         "HTTP_X_HEADER" => "header",
         "HTTP_AUTHORIZATION" => %{Token token="mytoken"},
         "HTTP_HOST" => "example.org",
-        "HTTP_COOKIES" => ""
+        "HTTP_COOKIES" => "",
+        "HTTP_SERVER" => nil
       }
     end
 
@@ -26,6 +27,7 @@
     it { should =~ /-H "Accept: application\/json"/ }
     it { should =~ /-H "X-Header: header"/ }
     it { should =~ /-H "Authorization: Token token=\\"mytoken\\""/ }
+    it { should =~ /-H "Server: "/ }
     it { should_not =~ /-H "Host: example\.org"/ }
     it { should_not =~ /-H "Cookies: "/ }