code: def fields(self) -> typing.Set[str]:
      # Returns a set with the fields set in `inject`.
      return self.formatter.fields
  
file_path: metaflow/metaflow/tracing/propagator.py
imports: import os
  import typing
  from opentelemetry.context import Context
  from opentelemetry.trace.propagation.tracecontext import TraceContextTextMapPropagator
  from opentelemetry.context.context import Context
  from opentelemetry.propagators.textmap import DefaultGetter, DefaultSetter, Getter, Setter, TextMapPropagator, CarrierT
label_desc: Use image node_id 6 for calling the EnvPropagator obj's underlying member method code with example usage: obj.fields() and returns: self