What causes "Empty function result {func}" in hcengineering/platform?

Fix the transform to return a valid value or a sensible default

hcengineering/platform · error · ProcessError

process.error.EmptyFunctionResult

process.error.EmptyFunctionResult

Error message

Empty function result {func}

What it means

Thrown when the transform function (sourceFunction) returns null/undefined and the primary function is not process.function.EmptyValue (which legitimately allows empty results). A required function chain produced no value.

Source

Thrown at server-plugins/process-resources/src/utils.ts:268

  const func = control.client.getModel().findObject(context.func)
  if (func === undefined) throw processError(process.error.MethodNotFound, { methodId: context.func }, {}, true)
  const impl = control.client.getHierarchy().as(func, serverProcess.mixin.FuncImpl)
  if (impl === undefined) throw processError(process.error.MethodNotFound, { methodId: context.func }, {}, true)
  const f = await getResource(impl.func)
  const res = await f(null, context.props, control, execution)
  if (context.sourceFunction !== undefined) {
    const transform = control.client.getModel().findObject(context.sourceFunction.func)
    if (transform === undefined) {
      throw processError(process.error.MethodNotFound, { methodId: context.sourceFunction.func }, {}, true)
    }
    if (!control.client.getHierarchy().hasMixin(transform, serverProcess.mixin.FuncImpl)) {
      throw processError(process.error.MethodNotFound, { methodId: context.sourceFunction.func }, {}, true)
    }
    const funcImpl = control.client.getHierarchy().as(transform, serverProcess.mixin.FuncImpl)
    const f = await getResource(funcImpl.func)
    const val = await f(res, {}, control, execution)
    if (val == null && context.func !== process.function.EmptyValue) {
      throw processError(process.error.EmptyFunctionResult, {}, { func: func.label })
    }
    return val
  }
  if (res == null && context.func !== process.function.EmptyValue) {
    throw processError(process.error.EmptyFunctionResult, {}, { func: func.label })
  }
  return res
}

function getUserRequestValue (control: ProcessControl, execution: Execution, context: SelectedUserRequest): any {
  const userContext = execution.context[context.id]
  if (userContext !== undefined) return userContext
  const attr = control.client.getHierarchy().findAttribute(context._class, context.key)
  throw processError(
    process.error.UserRequestedValueNotProvided,
    {},
    { attr: attr?.label ?? getEmbeddedLabel(context.key) }
  )

View on GitHub (pinned to 63e28dc964)

Solutions

Fix the transform to return a valid value or a sensible default
Check the primary function's output matches what the transform expects
Use process.function.EmptyValue as context.func if empty results are acceptable
Add logging in the transform to see the input res and returned val

Example fix

// before
const val = await f(res, {}, control, execution)
// after
const val = await f(res, {}, control, execution) ?? [] // explicit default instead of null

Defensive patterns

Strategy: try-catch

Validate before calling

const val = await transformFn(res, {}, control, execution)
if (val == null) {
  throw new Error(`transform returned no value for input ${JSON.stringify(res)}`)
}

Type guard

function isDefined<T>(v: T | null | undefined): v is T { return v !== null && v !== undefined }

Try / catch

try {
  val = await getContextValue(control, execution, context)
} catch (e) {
  if (e?.code === 'process.error.EmptyFunctionResult') {
    val = [] // or surface a user-facing 'no data' state
  } else throw e
}

Prevention

Return defaults instead of null from transform functions
Use process.function.EmptyValue when empty results are valid
Log transform inputs/outputs during development to spot null paths

When it happens

Trigger: val = await f(res, {}, control, execution) yields null while context.func !== EmptyValue — the transform filtered out all input or returned nothing for the given input.

Common situations: Transform's filter predicate matches nothing; upstream primary function returned data the transform does not handle; logic bug returning null instead of a default.

Related errors

AI-assisted analysis of hcengineering/platform@63e28dc964 (2026-08-29). Data as JSON: /api/errors/a78370cdc521f732. Report an issue: GitHub.