public Builder mergeStackTrace(com.google.devtools.cloudtrace.v2.StackTrace value) {
      if (stackTraceBuilder_ == null) {
        if (((bitField0_ & 0x00000080) != 0)
            && stackTrace_ != null
            && stackTrace_ != com.google.devtools.cloudtrace.v2.StackTrace.getDefaultInstance()) {
          getStackTraceBuilder().mergeFrom(value);
        } else {
          stackTrace_ = value;
        }
      } else {
        stackTraceBuilder_.mergeFrom(value);
      }
      if (stackTrace_ != null) {
        bitField0_ |= 0x00000080;
        onChanged();
      }
      return this;
    }
<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