cbimport CSV fails when --infer-types is used on a field that is "NAN"

Problem
cbimport CSV fails to import a document with when using --infer-types where a field is NaN. This is because NaN is a valid float under the IEEE-754 specification meaning Not a Number.

Steps to reproduce

1. Create the following CSV

   a,b

   100,NAN

2. Import the CSV

   cbimport csv -c couchbase://localhost -u Administrator -p password -b default -d file:///test.csv --field-separator , -g direct::#MONO_INCR# --omit-empty --infer-types

Expectation
For the import not to fail and for NAN to be treated as a string and not a float.