Remove trailing '?' on empty query. (#506)

Closes #464

src/request.rs

@@ -353,6 +353,11 @@ impl RequestBuilder {
                 error = Some(::error::from(err));
             }
         }
+        if let Ok(ref mut req) = self.request {
+            if let Some("") = req.url().query() {
+                req.url_mut().set_query(None);
+            }
+        }
         if let Some(err) = error {
             self.request = Err(err);
         }
@@ -837,4 +842,20 @@ mod tests {
         assert_eq!(foo[0], "bar");
         assert_eq!(foo[1], "baz");
     }
+
+    #[test]
+    fn normalize_empty_query() {
+        let client = Client::new();
+        let some_url = "https://google.com/";
+        let empty_query: &[(&str, &str)] = &[];
+
+        let req = client
+            .get(some_url)
+            .query(empty_query)
+            .build()
+            .expect("request build");
+
+        assert_eq!(req.url().query(), None);
+        assert_eq!(req.url().as_str(), "https://google.com/");
+    }
 }