public Builder mergeUpdateMask(com.google.protobuf.FieldMask value) {
      if (updateMaskBuilder_ == null) {
        if (((bitField0_ & 0x00000002) != 0)
            && updateMask_ != null
            && updateMask_ != com.google.protobuf.FieldMask.getDefaultInstance()) {
          getUpdateMaskBuilder().mergeFrom(value);
        } else {
          updateMask_ = value;
        }
      } else {
        updateMaskBuilder_.mergeFrom(value);
      }
      if (updateMask_ != null) {
        bitField0_ |= 0x00000002;
        onChanged();
      }
      return this;
    }
<pre>
Required. Field mask is used to specify the fields to be overwritten in the
`NetworkPolicy` resource by the update.
The fields specified in the `update_mask` are relative to the resource, not
the full request. A field will be overwritten if it is in the mask. If the
user does not provide a mask then all fields will be overwritten.
</pre>

<code>.google.protobuf.FieldMask update_mask = 2 [(.google.api.field_behavior) = REQUIRED];
</code>
java-vmwareengine/proto-google-cloud-vmwareengine-v1/src/main/java/com/google/cloud/vmwareengine/v1/UpdateNetworkPolicyRequest.java