You can use the design resource of the aura component bundle to control which attributes are exposed from lightning components to Flows.
Here is the developer document: Aura Component Bundle Design Resources
For instance, lets us say that you have a component attribute in this way,
<aura:component implements="lightning:availableForFlowScreens" access="global">
<!-- Component Attributes-->
<aura:attribute name="isCreateNewClientAcc" type="Boolean" />
You can expose this attribute to the flows by adding it to the design resource
<design:attribute name="isCreateNewClientAcc" Label="Is Create New Client Account?"/>
Now in the flow when you add the lightning component to the screen, you will find the "Is Create New Client Account?" in the Input/Output variables section.
You can assign appropriate flow variables. If you want to pass info from the flow to the lightning component send the flow variable value through the Input variable section, and if you want to pass a value from the component to the flow, then add a flow variable in the output section.
The example talks about a boolean variable, but in your case, you would create a flow variable of type collection and assign it similarly. Later you can use that flow variable in decisions to check if it is null or not.
Note: If you have already added the component to the screen and then you added the design resource to the aura component bundle, you need to refresh the flow to load the latest changes on the aura component.