public Builder clearSpanId() {
      spanId_ = getDefaultInstance().getSpanId();
      bitField0_ = (bitField0_ & ~0x00000002);
      onChanged();
      return this;
    }
<pre>
Required. The `[SPAN_ID]` portion of the span's resource name.
</pre>

<code>string span_id = 2 [(.google.api.field_behavior) = REQUIRED];</code>

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