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When dealing with optional, nullable, or possibly-missing values, handle them explicitly and avoid redundant or misleading fallback patterns:

• Don’t add unnecessary fallbacks when the language already handles the case safely. For example, spreading undefined is a no-op, so { ...args?.header } is sufficient; { ...(args?.header ?? {}) } is redundant.
• Avoid double-defaulting the same value (e.g. giving a default in a function parameter and again when destructuring it), since this can silently override values the caller actually passed:

  // Bad: options.all/options.dot already resolved before destructuring, can override caller's input
  const { all = options?.all ?? false, dot = options?.dot ?? false } = options
  
  // Good: single point of truth for defaults
  export const parseBody = async (
    request: HonoRequest | Request,
    options: ParseBodyOptions = {}
  ) => {
    const { all = false, dot = false } = options
    ...
  }
  

• Choose the correct operator based on the actual semantics needed. ?? only triggers on null/undefined, || also triggers on falsy values like '' or false. If an empty string or false is a meaningful, distinct value (e.g. “no header name” vs “use default header name”), handle it explicitly instead of relying on ??:

  // headerName === '' means "disable the feature", which `??` won't catch
  let requestId = headerName ? c.req.header(headerName) : undefined
  

• When narrowing a union of types that may or may not have a given optional property, prefer explicit discriminants (e.g. an in check or a type-guard function) over chained optional access, which can silently resolve to undefined even when the property exists under a different shape:

  // Bad: silently undefined for APIGatewayProxyEventV2
  method: event.httpMethod ?? event.requestContext.http?.httpMethod
  
  // Good: explicit discrimination between event shapes
  const method = 'httpMethod' in event ? event.httpMethod : event.requestContext.http.method
  

• Avoid the non-null assertion operator (!) to silence the type checker; prefer explicit null checks or restructuring the logic so TypeScript can narrow the type on its own.
• When a value may legitimately be absent, decide on and document one consistent representation (e.g. always return '' instead of mixing undefined/null/'') so the function’s return type stays predictable (e.g. string instead of string | undefined) and callers don’t need extra null checks.

Applying these practices prevents subtle bugs from incorrect fallback logic, keeps nullable/optional handling intentional, and reduces the need for non-null assertions and type casts.

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