Fix uninitialized error detection

error.go

@@ -91,7 +91,7 @@ func New(e interface{}) *Error {
 // fmt.Errorf("%v"). The skip parameter indicates how far up the stack
 // to start the stacktrace. 0 is from the current call, 1 from its caller, etc.
 func Wrap(e interface{}, skip int) *Error {
-	if e == nil {
+	if IsUninitialized(e) {
 		return nil
 	}
 
@@ -121,7 +121,7 @@ func Wrap(e interface{}, skip int) *Error {
 // up the stack to start the stacktrace. 0 is from the current call,
 // 1 from its caller, etc.
 func WrapPrefix(e interface{}, prefix string, skip int) *Error {
-	if e == nil {
+	if IsUninitialized(e) {
 		return nil
 	}
 
@@ -207,3 +207,17 @@ func (err *Error) TypeName() string {
 func (err *Error) Unwrap() error {
 	return err.Err
 }
+
+// IsUninitialized returns true if the error is nil or is zero value
+func IsUninitialized(i interface{}) bool {
+	if i == nil {
+		return true
+	}
+	switch reflect.TypeOf(i).Kind() {
+	case reflect.Struct:
+		return reflect.ValueOf(i).IsZero()
+	case reflect.Ptr, reflect.Map, reflect.Array, reflect.Chan, reflect.Slice:
+		return reflect.ValueOf(i).IsNil()
+	}
+	return false
+}

error_test.go

@@ -345,3 +345,42 @@ type errorString string
 func (e errorString) Error() string {
 	return string(e)
 }
+
+type errorStruct struct {
+	message string
+}
+
+func (e errorStruct) Error() string {
+	return e.message
+}
+
+type errorStructPtr struct {
+	message string
+}
+
+func (e *errorStructPtr) Error() string {
+	return e.message
+}
+
+func TestUninitializedErr(t *testing.T) {
+	var (
+		err          = error(nil)
+		errStruct    errorStruct
+		errStructPtr *errorStructPtr
+	)
+
+	err = WrapPrefix(err, "blah message", 0)
+	if err != (*Error)(nil) || !IsUninitialized(err) {
+		t.Errorf("Expected wrapped base error to be nil. Got %v", err)
+	}
+
+	err = WrapPrefix(errStruct, "blah message", 0)
+	if err != (*Error)(nil) || !IsUninitialized(err) {
+		t.Errorf("Expected wrapped errStruct to be nil. Got %v", err)
+	}
+
+	err = WrapPrefix(errStructPtr, "blah message", 0)
+	if err != (*Error)(nil) || !IsUninitialized(err) {
+		t.Errorf("Expected wrapped errStructPtr to be nil. Got %v", err)
+	}
+}