public final <R> Call<R> map(Mapper<V, R> mapper) {
    return new Mapping<>(mapper, this);
  }
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.
zipkin/src/main/java/zipkin2/Call.java