public Builder setParentSpanIdBytes(com.google.protobuf.ByteString value) {
      if (value == null) {
        throw new NullPointerException();
      }
      checkByteStringIsUtf8(value);
      parentSpanId_ = value;
      bitField0_ |= 0x00000004;
      onChanged();
      return this;
    }
<pre>
The `[SPAN_ID]` of this span's parent span. If this is a root span,
then this field must be empty.
</pre>

<code>string parent_span_id = 3;</code>

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