error when writing values from Node.js

[jiangts]

I tried the foreign values example, but am still getting

Cannot write

Error: Cannot write 
    at Error (native)
    at Object.com.cognitect.transit.impl.writer.emitMap (.../node_modules/transit-js/transit.js:2887:7)
    at Object.com.cognitect.transit.impl.writer.marshal (.../node_modules/transit-js/transit.js:2932:50)
    at Object.com.cognitect.transit.impl.writer.marshalTop (.../node_modules/transit-js/transit.js:2950:59)
    at com.cognitect.transit.impl.writer.Writer.write [as write] (.../node_modules/transit-js/transit.js:2962:231)
    ... 

The object I'm writing comes from an object returned by node-pg.

Any ideas of what's wrong?

Update: I found this post https://groups.google.com/forum/#!topic/transit-format/zGXBjF82Llg
Similar to his problem, if I roundtrip the data with JSON.stringify and JSON.parse, transit-js writes without error. However, that solution isn't very helpful as I lose all data type information in the JSON roundtrip...