apache/beam · error

empty graph

Error message

empty graph

What it means

graphx.Marshal converts a list of graph MultiEdges into a pipepb.Pipeline model pipeline. An empty edge list means there is no graph to convert, so Marshal rejects it up front with this error instead of emitting a degenerate pipeline.

Source

Thrown at sdks/go/pkg/beam/core/runtime/graphx/translate.go:185

	PipelineResourceHints resource.Hints

	// ContextReg is an override for the context extractor registry for testing.
	ContextReg *contextreg.Registry
}

// GetContextReg returns the default context registry if the option is
// unset, and the field version otherwise.
func (opts *Options) GetContextReg() *contextreg.Registry {
	if opts.ContextReg == nil {
		return contextreg.Default()
	}
	return opts.ContextReg
}

// Marshal converts a graph to a model pipeline.
func Marshal(edges []*graph.MultiEdge, opt *Options) (*pipepb.Pipeline, error) {
	if len(edges) == 0 {
		return nil, errors.New("empty graph")
	}

	tree := NewScopeTree(edges)

	m := newMarshaller(opt)
	for _, edge := range tree.Edges {
		_, err := m.addMultiEdge(edge)
		if err != nil {
			return nil, err
		}
	}
	for _, t := range tree.Children {
		_, err := m.addScopeTree(t)
		if err != nil {
			return nil, err
		}
	}

View on GitHub (pinned to 12126d8942)

Solutions

1. Add at least one PTransform/edge to the pipeline before marshaling.
2. Check the code path that builds the edges slice for logic that can drop all edges.
3. Guard call sites: verify len(edges) > 0 before calling Marshal.

Example fix

// before
pipeline, err := graphx.Marshal(edges, opts)
// after
if len(edges) == 0 { return nil, fmt.Errorf("pipeline has no transforms") }
pipeline, err := graphx.Marshal(edges, opts)

if len(edges) == 0 { return errors.New("cannot marshal: pipeline graph has no transforms") }

When it happens

Trigger: Calling Marshal (directly or via Expand/Execute paths) with a nil or zero-length edges slice — e.g. a constructed pipeline that produced no transforms, or a test passing an empty graph.

Common situations: Building a pipeline programmatically without adding any transforms before externalizing/running it; a filter/branch step eliminating all edges; unit tests exercising Marshal with empty input.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• empty type
• encoding partition function
• The pipeline has not been run.
• The pipeline contains abandoned PTransform(s).
• PCollections come from different Pipelines

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/fff3dcb07dee0c78. Report an issue: GitHub.