fix: gracefully handle nil err in Logger

This handles the case where a null error is passed into the Logger
without causing a null pointer dereference / segfault. There are
currently a couple places that invoke this function with a nil error and
were resulting in a segfault.

pkg/logging/logging.go

@@ -57,9 +57,11 @@ func (l *Logger) Error(err error, msg string, kvList ...interface{}) {
 		Args map[string]interface{}
 	}{
 		Msg:  msg,
-		Err:  err.Error(),
 		Args: map[string]interface{}{},
 	}
+	if err != nil {
+		payload.Err = err.Error()
+	}
 	if len(kvList)%2 != 0 {
 		kvList = append(kvList, "<no-value>")
 	}