Budibase/budibase · error

Cannot render an empty flow chain

Error message

Cannot render an empty flow chain

What it means

The FlowChart's render pipeline (getRenderResult, invoked by renderChain) computes layout for a chain of automation flow nodes and needs at least one node's source to anchor the rendering. When getLastSource returns undefined — meaning the chain context has no nodes — rendering cannot proceed and this error is thrown.

Source

Thrown at packages/builder/src/components/automation/AutomationBuilder/FlowChart/FlowCanvas/renderers/FlowChainRenderer.ts:105

const renderBlock = (step: AutomationBlock, context: ChainRenderContext) => {
  if (step.stepId === AutomationActionStepId.BRANCH) {
    renderBranchSplit(step, context)
    return false
  }

  if (isLoopV2Step(step)) {
    renderLoop(step, context)
    return true
  }

  renderStep(step, context)
  return true
}

const getRenderResult = (context: ChainRenderContext): ChainRenderResult => {
  const lastSource = getLastSource(context)
  if (!lastSource) {
    throw new Error("Cannot render an empty flow chain")
  }

  return {
    lastNodeId: lastSource.nodeId,
    lastNodeBlock: lastSource.block,
    bottomY: context.currentY,
    branched: context.branched,
    terminals: context.terminals,
  }
}

export const renderChain = (
  chain: AutomationBlock[],
  parentNodeId: string,
  parentBlock: FlowBlockContext,
  startY: number,
  deps: GraphBuildDeps
): ChainRenderResult => {

View on GitHub (pinned to a81a902e9a)

Solutions

1. Ensure the automation chain being rendered contains at least one node before calling renderChain.
2. Add a guard in the caller: skip rendering (or render an empty-state placeholder) when the node list is empty.
3. If nodes are filtered out upstream, keep the trigger/root node in the context so the chain is never empty.

Example fix

// before
renderChain(context) // context.nodes may be []
// after
if (context.nodes.length === 0) return renderEmptyState()
renderChain(context)

const canRenderChain = (ctx: ChainRenderContext): boolean =>
  getLastSource(ctx) != null // or: ctx.nodes.length > 0

if (!canRenderChain(context)) {
  return renderEmptyStatePlaceholder()
}
const result = renderChain(context)

const hasChainSource = (ctx: ChainRenderContext): ctx is ChainRenderContext & { nodes: [Node, ...Node[]] } =>
  ctx.nodes.length > 0

let result: ChainRenderResult
try {
  result = renderChain(context)
} catch (err) {
  if (err instanceof Error && err.message === "Cannot render an empty flow chain") {
    result = emptyChainRenderResult()
  } else throw err
}

When it happens

Trigger: renderChain called with a ChainRenderContext whose node list is empty — e.g. an automation with zero steps, a branch that filtered out all nodes, or a context constructed without seeding an initial node/block.

Common situations: Builder UI rendering an automation where the user deleted every step; a test or extension constructing a chain context manually and forgetting the first node; upstream filtering (enabled=false, block missing) removing all nodes before render.

Related errors

• Unexpected response ${response.statusText}
• No response received for attachment
• Unexpected response body stream type
• Invalid signed URL
• Source table '${relationship.sourceTable}' not found in data

AI-assisted analysis of Budibase/budibase@a81a902e9a (2026-08-29). Data as JSON: /api/errors/d89485c21ae2815c. Report an issue: GitHub.