prevent nil pointer exceptions on keys

Signed-off-by: Liam White <liam@tetrate.io>

pkg/manifest/locate.go

@@ -53,6 +53,9 @@ type Key struct {
 // The build version is searched for as a prefix of the OperatingSystemVersion.
 // If the OperatingSystemVersion is empty it returns the first build listed for that operating system
 func Locate(key *Key, manifestLocation string) (string, error) {
+	if key == nil {
+		return "", errors.New("passed key was nil")
+	}
 	if u, err := url.Parse(manifestLocation); err != nil || u.Host == "" || u.Scheme == "" {
 		return "", errors.New("only URL manifest locations are supported")
 	}

pkg/manifest/locate_test.go

@@ -61,13 +61,20 @@ func TestLocate(t *testing.T) {
 			responseStatusCode: http.StatusOK,
 			wantErr:            true,
 		},
+		{
+			name:      "Error if passed nil key",
+			reference: "notAReference",
+			wantErr:   true,
+		},
 		{
 			name:             "Error on non-url manifest locations",
+			reference:        "standard:1.11.0",
 			locationOverride: "not-a-url",
 			wantErr:          true,
 		},
 		{
 			name:               "Error on failed fetch",
+			reference:          "standard:1.11.0",
 			responseStatusCode: http.StatusTeapot,
 			wantErr:            true,
 		},