Fix candidatePair.String() nil pointer

Resolves #197

README.md

@@ -61,6 +61,7 @@ Check out the **[contributing wiki](https://github.com/pion/webrtc/wiki/Contribu
 * [ZHENK](https://github.com/scorpionknifes)
 * [Assad Obaid](https://github.com/assadobaid)
 * [Antoine Baché](https://github.com/Antonito)
+* [Will Forcey](https://github.com/wawesomeNOGUI)
 
 ### License
 MIT License - see [LICENSE](LICENSE) for full text

candidatepair.go

@@ -26,6 +26,10 @@ type candidatePair struct {
 }
 
 func (p *candidatePair) String() string {
+	if p == nil {
+		return ""
+	}
+
 	return fmt.Sprintf("prio %d (local, prio %d) %s <-> %s (remote, prio %d)",
 		p.Priority(), p.local.Priority(), p.local, p.remote, p.remote.Priority())
 }

candidatepair_test.go

@@ -122,3 +122,11 @@ func TestCandidatePairEquality(t *testing.T) {
 		t.Fatalf("Expected %v to equal %v", pairA, pairB)
 	}
 }
+
+func TestNilCandidatePairString(t *testing.T) {
+	var nilCandidatePair *candidatePair
+
+	if res := nilCandidatePair.String(); res != "" {
+		t.Fatalf("Expected %v to equal %v", res, "")
+	}
+}