[15:37:17] Cannot convert undefined or null to object
After checking the code, I found the root cause of this error. The error is caused by NPM package now-and-later, which is included in Debian package gulp version 4.0.2-2. The version included is 1.0.0. It should be upgraded to at least version 2.0.0. Gulp will not work with version 1.0.0 due to incompatible API change. After replacing the package with version 2.0.1 downloaded from NPM, the error disappears. Also, perhaps all those packages bundled with gulp should be in separate Debian packages instead.
