Don't log errors for unexpected Attachment parents for BodyContent objects with empty body

<object class="BodyContent" package="com.atlassian.confluence.core">
    <id name="id">407668675</id>
    <property name="body"></property>
    <property name="bodyType">2</property>
    <property name="content" class="Attachment" package="com.atlassian.confluence.pages"><id name="id">193343961</id></property>
</object> 

<object class="Attachment" package="com.atlassian.confluence.pages">
    <id name="id">193343961</id>
    <property name="hibernateVersion">40</property>
    <property name="title">XXX</property>
    <property name="lowerTitle">xxx</property>
    <property name="version">32</property>
    <property name="creationDate">2018-10-18 10:08:38.828</property>
    <property name="lastModificationDate">2018-10-18 10:08:38.828</property>
    <property name="versionComment"></property>
    <property name="contentStatus">current</property>
    <property name="creator" class="ConfluenceUserImpl" package="com.atlassian.confluence.user"><id name="key">000000005a08e724015a475cf28111fb</id></property>
    <property name="lastModifier" class="ConfluenceUserImpl" package="com.atlassian.confluence.user"><id name="key">000000005a08e724015a475cf28111fb</id></property>
    <property name="containerContent" class="Page" package="com.atlassian.confluence.pages"><id name="id">193344021</id></property>
    <property name="space" class="Space" package="com.atlassian.confluence.spaces"><id name="id">115507201</id></property>
    <collection name="contentProperties" class="java.util.Collection">
        <element class="ContentProperty" package="com.atlassian.confluence.content"><id name="id">193692170</id></element>
        <element class="ContentProperty" package="com.atlassian.confluence.content"><id name="id">212615172</id></element>
        <element class="ContentProperty" package="com.atlassian.confluence.content"><id name="id">301636544</id></element>
    </collection>
</object>

Unexpected type [Attachment] for parent object id [193343961]. This is a bug in confluence-xml, please report