public Builder mergePreparingVmDisks(
        com.google.cloud.vmmigration.v1.PreparingVMDisksStep value) {
      if (preparingVmDisksBuilder_ == null) {
        if (stepCase_ == 6
            && step_ != com.google.cloud.vmmigration.v1.PreparingVMDisksStep.getDefaultInstance()) {
          step_ =
              com.google.cloud.vmmigration.v1.PreparingVMDisksStep.newBuilder(
                      (com.google.cloud.vmmigration.v1.PreparingVMDisksStep) step_)
                  .mergeFrom(value)
                  .buildPartial();
        } else {
          step_ = value;
        }
        onChanged();
      } else {
        if (stepCase_ == 6) {
          preparingVmDisksBuilder_.mergeFrom(value);
        } else {
          preparingVmDisksBuilder_.setMessage(value);
        }
      }
      stepCase_ = 6;
      return this;
    }
<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