public Builder mergeBuildId(com.google.devtools.cloudtrace.v2.TruncatableString value) {
      if (buildIdBuilder_ == null) {
        if (((bitField0_ & 0x00000002) != 0)
            && buildId_ != null
            && buildId_
                != com.google.devtools.cloudtrace.v2.TruncatableString.getDefaultInstance()) {
          getBuildIdBuilder().mergeFrom(value);
        } else {
          buildId_ = value;
        }
      } else {
        buildIdBuilder_.mergeFrom(value);
      }
      if (buildId_ != null) {
        bitField0_ |= 0x00000002;
        onChanged();
      }
      return this;
    }
<pre>
A unique identifier for the module, usually a hash of its
contents (up to 128 bytes).
</pre>

<code>.google.devtools.cloudtrace.v2.TruncatableString build_id = 2;</code>
java-trace/proto-google-cloud-trace-v2/src/main/java/com/google/devtools/cloudtrace/v2/Module.java