private com.google.protobuf.SingleFieldBuilderV3<
              com.google.devtools.cloudtrace.v2.Span.Attributes,
              com.google.devtools.cloudtrace.v2.Span.Attributes.Builder,
              com.google.devtools.cloudtrace.v2.Span.AttributesOrBuilder>
          getAttributesFieldBuilder() {
        if (attributesBuilder_ == null) {
          attributesBuilder_ =
              new com.google.protobuf.SingleFieldBuilderV3<
                  com.google.devtools.cloudtrace.v2.Span.Attributes,
                  com.google.devtools.cloudtrace.v2.Span.Attributes.Builder,
                  com.google.devtools.cloudtrace.v2.Span.AttributesOrBuilder>(
                  getAttributes(), getParentForChildren(), isClean());
          attributes_ = null;
        }
        return attributesBuilder_;
      }
<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