Merge PR #1281: Don't run defers if it would result in an NPE

* Don't run defers if it would result in an NPE
* Nuke CircleCI caches

server/start_test.go

@@ -18,6 +18,7 @@ import (
 
 func TestStartStandAlone(t *testing.T) {
 	home, err := ioutil.TempDir("", "mock-sdk-cmd")
+	require.Nil(t, err)
 	defer func() {
 		os.RemoveAll(home)
 	}()

server/test_helpers.go

@@ -18,10 +18,10 @@ import (
 // protocol is either tcp, http, etc
 func FreeTCPAddr() (addr, port string, err error) {
 	l, err := net.Listen("tcp", "0.0.0.0:0")
-	defer l.Close()
 	if err != nil {
 		return "", "", err
 	}
+	defer l.Close()
 
 	portI := l.Addr().(*net.TCPAddr).Port
 	port = fmt.Sprintf("%d", portI)