# `Cucumber.UndefinedParameterTypeError`
[🔗](https://github.com/huddlz-hq/cucumber/blob/main/lib/cucumber/undefined_parameter_type_error.ex#L1)

Raised when a step pattern references a parameter type that is neither a
built-in nor a registered custom type (see `Cucumber.ParameterTypes`).

During discovery, step definitions with undefined parameter types are
excluded from the registry with a warning — steps that would have matched
them fail as undefined, mirroring reference Cucumber implementations. This
exception surfaces when such a pattern is compiled directly via
`Cucumber.Expression.compile/2`.

# `t`

```elixir
@type t() :: %Cucumber.UndefinedParameterTypeError{
  __exception__: term(),
  message: String.t(),
  pattern: String.t() | nil,
  type_name: String.t()
}
```

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*Consult [api-reference.md](api-reference.md) for complete listing*