private com.google.protobuf.SingleFieldBuilderV3<
            com.google.cloud.vmmigration.v1.PreparingVMDisksStep,
            com.google.cloud.vmmigration.v1.PreparingVMDisksStep.Builder,
            com.google.cloud.vmmigration.v1.PreparingVMDisksStepOrBuilder>
        getPreparingVmDisksFieldBuilder() {
      if (preparingVmDisksBuilder_ == null) {
        if (!(stepCase_ == 6)) {
          step_ = com.google.cloud.vmmigration.v1.PreparingVMDisksStep.getDefaultInstance();
        }
        preparingVmDisksBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.cloud.vmmigration.v1.PreparingVMDisksStep,
                com.google.cloud.vmmigration.v1.PreparingVMDisksStep.Builder,
                com.google.cloud.vmmigration.v1.PreparingVMDisksStepOrBuilder>(
                (com.google.cloud.vmmigration.v1.PreparingVMDisksStep) step_,
                getParentForChildren(),
                isClean());
        step_ = null;
      }
      stepCase_ = 6;
      onChanged();
      return preparingVmDisksBuilder_;
    }
<pre>
Preparing VM disks step.
</pre>

<code>.google.cloud.vmmigration.v1.PreparingVMDisksStep preparing_vm_disks = 6;</code>
java-vmmigration/proto-google-cloud-vmmigration-v1/src/main/java/com/google/cloud/vmmigration/v1/CutoverStep.java