public Builder clearSpanId() {
        spanId_ = getDefaultInstance().getSpanId();
        bitField0_ = (bitField0_ & ~0x00000002);
        onChanged();
        return this;
      }
<pre>
The `[SPAN_ID]` for a span within a trace.
</pre>

<code>string span_id = 2;</code>

@return This builder for chaining.
java-trace/proto-google-cloud-trace-v2/src/main/java/com/google/devtools/cloudtrace/v2/Span.java