public Builder mergeCustomerEncryptionKey(
        com.google.cloud.tpu.v2alpha1.CustomerEncryptionKey value) {
      if (customerEncryptionKeyBuilder_ == null) {
        if (((bitField0_ & 0x00000001) != 0)
            && customerEncryptionKey_ != null
            && customerEncryptionKey_
                != com.google.cloud.tpu.v2alpha1.CustomerEncryptionKey.getDefaultInstance()) {
          getCustomerEncryptionKeyBuilder().mergeFrom(value);
        } else {
          customerEncryptionKey_ = value;
        }
      } else {
        customerEncryptionKeyBuilder_.mergeFrom(value);
      }
      if (customerEncryptionKey_ != null) {
        bitField0_ |= 0x00000001;
        onChanged();
      }
      return this;
    }
<pre>
Optional. Customer encryption key for boot disk.
</pre>

<code>
.google.cloud.tpu.v2alpha1.CustomerEncryptionKey customer_encryption_key = 1 [(.google.api.field_behavior) = OPTIONAL];
</code>
java-tpu/proto-google-cloud-tpu-v2alpha1/src/main/java/com/google/cloud/tpu/v2alpha1/BootDiskConfig.java