code: public final <R> Call<R> map(Mapper<V, R> mapper) {
      return new Mapping<>(mapper, this);
    }
docs: Maps the result of this call into a different shape, as defined by the {@code mapper} function.
  This is used to convert values from one type to another. For example, you could use this to
  convert between zipkin v1 and v2 span format.
  
  <pre>{@code
  getTracesV1Call = getTracesV2Call.map(traces -> v2TracesConverter);
  }</pre>
  
  <p>This method intends to be used for chaining. That means "this" instance should be discarded
  in favor of the result of this method.