ent/ent · error

graphson.RawMessage: UnmarshalGraphson on nil pointer

Error message

graphson.RawMessage: UnmarshalGraphson on nil pointer

What it means

UnmarshalGraphson is defined on a *RawMessage, and Go allows calling methods through a nil pointer receiver. This guard fires when the method is invoked on a nil *RawMessage, i.e. the caller never allocated the RawMessage (or holds a nil interface/pointer) before asking it to absorb the decoded bytes. The offending input is the nil receiver m, not the data argument.

Source

Thrown at dialect/gremlin/encoding/graphson/raw.go:31

// RawMessage must implement Marshaler/Unmarshaler interfaces.
var (
	_ Marshaler   = (*RawMessage)(nil)
	_ Unmarshaler = (*RawMessage)(nil)
)

// MarshalGraphson returns m as the graphson encoding of m.
func (m RawMessage) MarshalGraphson() ([]byte, error) {
	if m == nil {
		return []byte("null"), nil
	}
	return m, nil
}

// UnmarshalGraphson sets *m to a copy of data.
func (m *RawMessage) UnmarshalGraphson(data []byte) error {
	if m == nil {
		return errors.New("graphson.RawMessage: UnmarshalGraphson on nil pointer")
	}
	*m = append((*m)[0:0], data...)
	return nil
}

View on GitHub (pinned to 69d5d4deb1)

Solutions

1. Initialize the value: `m := graphson.RawMessage{}` and call on the addressable value, or `m = &graphson.RawMessage{}`
2. Use a non-pointer `graphson.RawMessage` field/type in your target struct

Example fix

// before
var m *graphson.RawMessage
m.UnmarshalGraphson(data)
// after
m := &graphson.RawMessage{}
m.UnmarshalGraphson(data)

if m == nil { return errors.New("RawMessage receiver must be initialized") }

func safeUnmarshal(m *graphson.RawMessage, data []byte) error {
  if m == nil { m = &graphson.RawMessage{} }
  return m.UnmarshalGraphson(data)
}

if err := m.UnmarshalGraphson(data); err != nil {
  return fmt.Errorf("raw graphson: %w", err)
}

When it happens

Trigger: Declaring `var m *graphson.RawMessage` (nil pointer) and calling `m.UnmarshalGraphson(data)`; having a struct field of type *RawMessage left nil when the decoder calls into it.

Common situations: Using a pointer-to-pointer or nil struct field in a response type; forgetting to initialize a RawMessage field before decoding.

Related errors

• expect map element, but found only key
• missing type or value
• cannot unmarshal into a nil pointer
• cannot read first list element: %w
• cannot unmarshal first map item: %w

AI-assisted analysis of ent/ent@69d5d4deb1 (2026-09-03). Data as JSON: /api/errors/d39d924c2751ab4b. Report an issue: GitHub.