public Builder setSpanIdBytes(com.google.protobuf.ByteString value) {
        if (value == null) {
          throw new NullPointerException();
        }
        checkByteStringIsUtf8(value);
        spanId_ = value;
        bitField0_ |= 0x00000002;
        onChanged();
        return this;
      }
<pre>
The `[SPAN_ID]` for a span within a trace.
</pre>

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

@param value The bytes for spanId to set.
@return This builder for chaining.
java-trace/proto-google-cloud-trace-v2/src/main/java/com/google/devtools/cloudtrace/v2/Span.java