When optional fields having "alphanumeric" type in an ACH file are left empty, nACHError is thrown with "Invalid data type" message

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For example, if the 'Reference Code' field in the File Header is left empty, a nACHError is thrown even though the file is in the correct format.
The issue seems to be with alphanumericRegex specified in lib.validate.js. It does not recognize empty strings

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I overcame it by changing the regex to alphanumericRegex = /(^[0-9a-zA-Z!"#$%&'()*+,-.\/:;<>=?@\[\]\\^_`{}|~ ]+$)|(^$)/