static assertNoDuplicateStrings(strings, arrayName) {
    const foundStrings = new Set();
    for (const string of strings) {
      if (foundStrings.has(string)) {
        throw new Error(`${arrayName} has duplicate entry of type '${string}'`);
      }
      foundStrings.add(string);
    }
  }
Asserts that `strings` has no duplicate strings in it, throwing an error if
it does. `arrayName` is included for nicer logging.
@param {Array<string>} strings
@param {string} arrayName