cli-plugins/manager: wrapAsPluginError: don't special-case nil

This was a pattern inheritted from pkg/errors.Wrapf, which ignored
nil errors for convenience. However, it is error-prone, as it is
not obvious when returning a nil-error.

All call-sites using `wrapAsPluginError` already do a check for
nil errors, so remove this code to prevent hard to find bugs.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
(cherry picked from commit 50963accec)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli-plugins/manager/error.go

@@ -36,9 +36,6 @@ func (e *pluginError) MarshalText() (text []byte, err error) {
 // wrapAsPluginError wraps an error in a pluginError with an
 // additional message.
 func wrapAsPluginError(err error, msg string) error {
-	if err == nil {
-		return nil
-	}
 	return &pluginError{cause: fmt.Errorf("%s: %w", msg, err)}
 }
 

cli-plugins/manager/error_test.go

@@ -21,4 +21,7 @@ func TestPluginError(t *testing.T) {
 	actual, err := json.Marshal(err)
 	assert.Check(t, err)
 	assert.Check(t, is.Equal(`"wrapping: testing"`, string(actual)))
+
+	err = wrapAsPluginError(nil, "wrapping")
+	assert.Check(t, is.Error(err, "wrapping: %!w(<nil>)"))
 }