diff --git a/src/index.js b/src/index.js
index d68e686..cde8c28 100644
--- a/src/index.js
+++ b/src/index.js
@@ -84,17 +84,17 @@ function convertDataAndConfigToConfig (method, data, config) {
   if (methodsWithConfigsAsSecondArg.includes(method)) {
     return validateconfig(method, data || {});
   } else {
-    return validateconfig(method, Object.assign({}, config || {}, { data: data }));
+    return validateconfig(method, Object.assign({}, config, { data: data }));
   }
 }
 
-var allowedConfigs = ['headers', 'params', 'data'];
+var allowedConfigProperties = ['headers', 'params', 'data'];
 function validateconfig (method, config) {
   for (var key in config) {
-    if (!allowedConfigs.includes(key)) {
+    if (!allowedConfigProperties.includes(key)) {
       throw new Error(
-        'Invalid config attribute ' +
-        key +
+        'Invalid config property ' +
+        JSON.stringify(key) +
         ' provided to ' +
         toMethodName(method) +
         '. Config: ' +
diff --git a/src/utils.js b/src/utils.js
index 59916ef..ba06240 100644
--- a/src/utils.js
+++ b/src/utils.js
@@ -166,7 +166,12 @@ function createAxiosError(message, config, response, code) {
 function createCouldNotFindMockError(config) {
   var message =
     "Could not find mock for: \n" +
-    JSON.stringify(config, ["method", "url"], 2);
+    JSON.stringify({
+      method: config.method,
+      url: config.url,
+      params: config.params,
+      headers: config.headers
+    }, null, 2);
   var error = new Error(message);
   error.isCouldNotFindMockError = true;
   error.url = config.url;