@Injectable can throw cannot read property of undefined error

[etsuo]

Injectable code:

export function getDependencyInjections(target: any, t: any, sapi: SakuraApi) {
  const expectedDiArgs = Reflect.getMetadata('design:paramtypes', t);

  const diArgs = [];

  for (const arg of expectedDiArgs || []) {
    debug(`injecting ${arg.name} into ${target.name}`);

    const isInjectable = !!arg[injectableSymbols.isSakuraApiInjectable];
    if (typeof arg !== 'function' || !isInjectable) {
      throw new NonInjectableConstructorParameterError(arg, target);
    }

    debug('\t getting provider from sapi');
    diArgs.push(sapi.getProvider(arg));
  }

  return diArgs;
}

• debug should not assume arg is instantiated (debugs should never throw errors in code).
• If arg is undefined, it should throw NonInjectableConstructorParameterError (see [1] below). -- It is likely this is because of a circular dependency -- notify the integrator this might be the case
• NonInjectableConstructorParameterError needs to be updated so that it returns the raw target if it's falsy so that the error message is properly rendered as: Error: Unable to inject undefined into SomeService. Only classes decorated with '@Injectable' can be passed into the SalesforceService constructor. -- right now it's reporting Object when it's undefined, which obfuscates what's actually happening. See [2] below:

[1] (transpiled output)

function getDependencyInjections(target, t, sapi) {
  const expectedDiArgs = Reflect.getMetadata('design:paramtypes', t);
  const diArgs = [];

  for (const arg of expectedDiArgs || []) {
    if (!arg) {
      throw new NonInjectableConstructorParameterError(arg, target);
    }

    debug(`injecting ${arg.name} into ${target.name}`);
    const isInjectable = !!arg[exports.injectableSymbols.isSakuraApiInjectable];
    if (typeof arg !== 'function' || !isInjectable) {
      throw new NonInjectableConstructorParameterError(arg, target);
    }
    debug('\t getting provider from sapi');
    diArgs.push(sapi.getProvider(arg));
  }
  return diArgs;
}

[2] (transpiled output)

class NonInjectableConstructorParameterError extends Error {

  constructor(target, source) {

    const targetName = (!target) ? target : (target || {}).name
      || ((target || {}).constructor || {}).name
      || typeof target;
    const sourceName = (source || {}).name
      || ((source || {}).constructor || {}).name
      || typeof source;
    const message = `Unable to inject ${targetName} into ${sourceName}. Only classes decorated with '@Injectable' can`
      + ` be passed into the ${sourceName} constructor.`;
    super(message);
  }
}