EntityMalformedException: Missing bundle property on entity of type node. in entity_extract_ids

In an Open Atrium installation I frequently encounter the error EntityMalformedException caused by the Comment Alter module.
The error is raised from comment_alter_get_changed_fields where the $old_node and/or $new_node are false. If these are false the call to diff_compare_entities() result in the mentioned EntityMalformedException error.

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