private com.google.protobuf.RepeatedFieldBuilderV3<
            com.google.devtools.cloudtrace.v2.Span,
            com.google.devtools.cloudtrace.v2.Span.Builder,
            com.google.devtools.cloudtrace.v2.SpanOrBuilder>
        getSpansFieldBuilder() {
      if (spansBuilder_ == null) {
        spansBuilder_ =
            new com.google.protobuf.RepeatedFieldBuilderV3<
                com.google.devtools.cloudtrace.v2.Span,
                com.google.devtools.cloudtrace.v2.Span.Builder,
                com.google.devtools.cloudtrace.v2.SpanOrBuilder>(
                spans_, ((bitField0_ & 0x00000002) != 0), getParentForChildren(), isClean());
        spans_ = null;
      }
      return spansBuilder_;
    }
<pre>
Required. A list of new spans. The span names must not match existing
spans, otherwise the results are undefined.
</pre>

<code>
repeated .google.devtools.cloudtrace.v2.Span spans = 2 [(.google.api.field_behavior) = REQUIRED];
</code>
java-trace/proto-google-cloud-trace-v2/src/main/java/com/google/devtools/cloudtrace/v2/BatchWriteSpansRequest.java