String interpolation errors (only with logback.xml)

Hello,

I am using Gatling 2.3 with a simple custom feeder (Map with two keys CreatedAt, Payload) and the following request body:


StringBody("""{ "created_at": "${CreatedAt}", "payload": "${Payload}" }""")

Running a simulation the output looks like this:

`

18:42:56.263 [ERROR] i.g.h.a.s.HttpRequestAction - ‘httpRequest-4’ failed to execute: No attribute named ‘CreatedAt’ is defined