zlib callback throws error which cannot be captured by caller

[zyf0330]

Code is at

saml2/lib/saml2.coffee

Line 566 in fca725b

_(uri.query).extend sign_request(deflated.toString('base64'), @private_key, options.relay_state)

If pass empty string private_key to SP, this code will throw error but cannot be captured by caller, just by process.uncaughtException. I think it should be captured and pass into callback.