public Builder mergeBootDiskConfig(com.google.cloud.tpu.v2alpha1.BootDiskConfig value) {
      if (bootDiskConfigBuilder_ == null) {
        if (((bitField0_ & 0x04000000) != 0)
            && bootDiskConfig_ != null
            && bootDiskConfig_
                != com.google.cloud.tpu.v2alpha1.BootDiskConfig.getDefaultInstance()) {
          getBootDiskConfigBuilder().mergeFrom(value);
        } else {
          bootDiskConfig_ = value;
        }
      } else {
        bootDiskConfigBuilder_.mergeFrom(value);
      }
      if (bootDiskConfig_ != null) {
        bitField0_ |= 0x04000000;
        onChanged();
      }
      return this;
    }
<pre>
Optional. Boot disk configuration.
</pre>

<code>
.google.cloud.tpu.v2alpha1.BootDiskConfig boot_disk_config = 49 [(.google.api.field_behavior) = OPTIONAL];
</code>
java-tpu/proto-google-cloud-tpu-v2alpha1/src/main/java/com/google/cloud/tpu/v2alpha1/Node.java