static void writeBinaryAnnotation(String key, String value, @Nullable byte[] endpoint,
    WriteBuffer b) {
    b.writeAscii("{\"key\":\"");
    b.writeUtf8(jsonEscape(key));
    b.writeAscii("\",\"value\":\"");
    b.writeUtf8(jsonEscape(value));
    b.writeByte('"');
    if (endpoint != null) {
      b.writeAscii(",\"endpoint\":");
      b.write(endpoint);
    }
    b.writeAscii("}");
  }
This type is only used to backport the v1 read api as it returns v1 json.
zipkin/src/main/java/zipkin2/internal/V1SpanWriter.java