Initialise Headers map to avoid runtime panic when purging. (#267)

* Initialise Headers map to avoid runtime panic when purging.

* tweak test comment

* Use project idioms.

fastly/purge.go

@@ -26,10 +26,13 @@ func (c *Client) Purge(i *PurgeInput) (*Purge, error) {
 		return nil, ErrMissingURL
 	}
 
-	ro := new(RequestOptions)
-	ro.Parallel = true
+	ro := &RequestOptions{
+		Parallel: true,
+	}
 	if i.Soft {
-		ro.Headers["Fastly-Soft-Purge"] = "1"
+		ro.Headers = map[string]string{
+			"Fastly-Soft-Purge": "1",
+		}
 	}
 
 	resp, err := c.Post("purge/"+i.URL, ro)

fastly/purge_test.go

@@ -1,10 +1,32 @@
 package fastly
 
-import "testing"
+import (
+	"testing"
+)
 
+// TestClient_Purge validates no runtime panics are raised by the Purge method.
+//
+// Specifically, we're ensuring that the setting of the `Soft` key to `true`
+// (which will require assigning a header to the RequestOptions.Headers field)
+// doesn't cause `panic: assignment to entry in nil map`.
 func TestClient_Purge(t *testing.T) {
 	t.Parallel()
 
+	client := DefaultClient()
+	url := "http://gofastly.fastly-testing.com/foo/bar"
+
+	_, err := client.Purge(&PurgeInput{
+		URL:  url,
+		Soft: true,
+	})
+	if err == nil {
+		t.Fatalf("we've accidentally purged a real URL: %s", url)
+	}
+}
+
+func TestClient_PurgeKey(t *testing.T) {
+	t.Parallel()
+
 	var err error
 	var purge *Purge
 	record(t, "purges/purge_by_key", func(c *Client) {