private com.google.protobuf.SingleFieldBuilderV3<
            com.google.devtools.cloudtrace.v2.StackTrace,
            com.google.devtools.cloudtrace.v2.StackTrace.Builder,
            com.google.devtools.cloudtrace.v2.StackTraceOrBuilder>
        getStackTraceFieldBuilder() {
      if (stackTraceBuilder_ == null) {
        stackTraceBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.devtools.cloudtrace.v2.StackTrace,
                com.google.devtools.cloudtrace.v2.StackTrace.Builder,
                com.google.devtools.cloudtrace.v2.StackTraceOrBuilder>(
                getStackTrace(), getParentForChildren(), isClean());
        stackTrace_ = null;
      }
      return stackTraceBuilder_;
    }
<pre>
Stack trace captured at the start of the span.
</pre>

<code>.google.devtools.cloudtrace.v2.StackTrace stack_trace = 8;</code>
java-trace/proto-google-cloud-trace-v2/src/main/java/com/google/devtools/cloudtrace/v2/Span.java