@java.lang.Override
    public void writeTo(com.google.protobuf.CodedOutputStream output) throws java.io.IOException {
      if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(traceId_)) {
        com.google.protobuf.GeneratedMessageV3.writeString(output, 1, traceId_);
      }
      if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(spanId_)) {
        com.google.protobuf.GeneratedMessageV3.writeString(output, 2, spanId_);
      }
      if (type_ != com.google.devtools.cloudtrace.v2.Span.Link.Type.TYPE_UNSPECIFIED.getNumber()) {
        output.writeEnum(3, type_);
      }
      if (((bitField0_ & 0x00000001) != 0)) {
        output.writeMessage(4, getAttributes());
      }
      getUnknownFields().writeTo(output);
    }
<pre>
A set of attributes on the link. Up to 32 attributes can be
specified per link.
</pre>

<code>.google.devtools.cloudtrace.v2.Span.Attributes attributes = 4;</code>
java-trace/proto-google-cloud-trace-v2/src/main/java/com/google/devtools/cloudtrace/v2/Span.java