More changes to probe to avoid nil dereferences

pkg/probe/probe.go

@@ -78,6 +78,10 @@ func New(e error) *Error {
 // Trace records the point at which it is invoked. Stack traces are important for
 // debugging purposes.
 func (e *Error) Trace(fields ...string) *Error {
+	if e == nil {
+		return nil
+	}
+
 	e.lock.Lock()
 	defer e.lock.Unlock()
 
@@ -103,6 +107,9 @@ func (e *Error) trace(fields ...string) *Error {
 
 // Untrace erases last trace entry.
 func (e *Error) Untrace() {
+	if e == nil {
+		return
+	}
 	e.lock.Lock()
 	defer e.lock.Unlock()
 
@@ -116,14 +123,21 @@ func (e *Error) Untrace() {
 
 // Error returns error string.
 func (e *Error) Error() string {
+	if e == nil {
+		return "<nil>"
+	}
 	return e.String()
 }
 
 // String returns error message.
 func (e *Error) String() string {
+	if e == nil {
+		return "<nil>"
+	}
 	e.lock.RLock()
 	defer e.lock.RUnlock()
 
+	if e.e != nil {
 		trace := e.e.Error() + "\n"
 		for i, tp := range e.tracePoints {
 			if len(tp.Env) > 0 {
@@ -142,9 +156,15 @@ func (e *Error) String() string {
 
 		return trace
 	}
+	return "<nil>"
+}
 
 // JSON returns JSON formated error trace.
 func (e *Error) JSON() string {
+	if e == nil {
+		return "<nil>"
+	}
+
 	e.lock.RLock()
 	defer e.lock.RUnlock()