Handle nil receiver in DataError.Unwrap safely

Author: tomas-novotny

error.go

@@ -130,6 +130,10 @@ func (e *DataError) WithCause(err error) *DataError {
 // Unwrap returns the cause if one was set via WithCause; otherwise it returns
 // the underlying error created by New, Newf, or Wrap.
 func (e *DataError) Unwrap() error {
+	if e == nil {
+		return nil
+	}
+
 	if e.cause != nil {
 		return e.cause
 	}

wrap_test.go

@@ -14,6 +14,13 @@ func TestWrapUnwrap(t *testing.T) {
 
 	assert.Equal(t, Unwrap(outer), inner)
 	assert.Equal(t, Unwrap(inner), nil)
+	assert.Equal(t, Unwrap(nil), nil)
+
+	var err *DataError
+	assert.Equal(t, Unwrap(err), nil)
+
+	var errs *MultiError
+	assert.Equal(t, Unwrap(errs), nil)
 }
 
 func TestWrapIs(t *testing.T) {
@@ -22,6 +29,13 @@ func TestWrapIs(t *testing.T) {
 
 	assert.True(t, Is(outer, inner))
 	assert.False(t, Is(outer, errors.New("other")))
+	assert.False(t, Is(nil, inner))
+
+	var err *DataError
+	assert.False(t, Is(err, inner))
+
+	var errs *MultiError
+	assert.False(t, Is(errs, inner))
 }
 
 func TestWrapAs(t *testing.T) {
@@ -31,4 +45,32 @@ func TestWrapAs(t *testing.T) {
 	var target *DataError
 	assert.True(t, As(wrapped, &target))
 	assert.Equal(t, target, original)
+
+	assert.False(t, As(nil, &target))
+
+	var nilErr *DataError
+	assert.True(t, As(nilErr, &target))
+	assert.Equal(t, target, nilErr)
+
+	var multiTarget *MultiError
+	var nilMulti *MultiError
+	assert.True(t, As(nilMulti, &multiTarget))
+	assert.Equal(t, multiTarget, nilMulti)
+}
+
+func TestWrapAsType(t *testing.T) {
+	original := New("test").WithField("k", "v")
+	wrapped := fmt.Errorf("wrapped: %w", original)
+
+	target, ok := AsType[*DataError](wrapped)
+	assert.True(t, ok)
+	assert.Equal(t, target, original)
+
+	_, ok = AsType[*DataError](nil)
+	assert.False(t, ok)
+
+	var nilErr *DataError
+	nilTarget, ok := AsType[*DataError](nilErr)
+	assert.True(t, ok)
+	assert.Equal(t, nilTarget, nilErr)
 }