code: function FundingError(msg, available, required) {
    Error.call(this);
  
    this.type = 'FundingError';
    this.message = msg;
    this.availableFunds = -1;
    this.requiredFunds = -1;
  
    if (available != null) {
      this.message += ` (available=${Amount.wmcc(available)},`;
      this.message += ` required=${Amount.wmcc(required)})`;
      this.availableFunds = available;
      this.requiredFunds = required;
    }
  
    if (Error.captureStackTrace)
      Error.captureStackTrace(this, FundingError);
  }
docs: An error thrown from the coin selector.
  @constructor
  @ignore
  @extends Error
  @param {String} msg
  @param {Amount} available
  @param {Amount} required
  @property {String} message - Error message.
  @property {Amount} availableFunds
  @property {Amount} requiredFunds