What is the proper condition to check for a select list value of none? I have a rule in drupal that populates an entity reference in a parent node with a child node. 

Then I created a new rule that is applied "before content is saved" that will remove the child node from the old parent node if one wants to move it to a different parent node. 

And it works as expected UNLESS one chooses -none- in the select list. How do I make it remove the child reference when none is selected. I tried Data value is empty and that doesn't work. 

Here is an export of my current rule: 

{ "rules_remove_job_from_client" : {
"LABEL" : "Remove Job From Client",
"PLUGIN" : "reaction rule",
"OWNER" : "rules",
"REQUIRES" : [ "rules" ],
"ON" : { "node_presave--job" : { "bundle" : "job" } },
"IF" : [
  { "NOT data_is" : {
      "data" : [ "node-unchanged:field-client" ],
      "value" : [ "node:field-client" ]
    }
  },
  { "node_is_of_type" : {
      "node" : [ "node:field-client" ],
      "type" : { "value" : { "clients" : "clients" } }
    }
  }
],
"DO" : [
  { "list_remove" : {
      "list" : [ "node-unchanged:field-client:field-all-jobs" ],
      "item" : [ "node-unchanged" ]
    }
  },
  { "drupal_message" : { "message" : "Is this firing" } }
]
}
}
Make sure to add a Rules condition Entity has field (related to your field field-client as shown in your first Rules Condition). For a video tutorial that illustrates the importance of this Entity has field condition, refer to Data types and data selection, especially what is shown between about 13:30 and 17:30 in it.

If that doesn't help, you may want to do some Rules debugging, as explained in the answer to "How can I display the value of a variable inside a condition?".