7 – Send an email to the product owner with the rules only when the email address is available

As a follow-up to the previous questions asked by me:
Send a mail to the product owner with the rules and retrieve the customer profile from the line items. I have the following question.

I've created a rule to send an email to the product owner in my online store. The email address is manually added to the product in a custom field. The rule works when the e-mail address is available, but when it is not available, an error is generated. How can I check if the e-mail address is there and then only send the e-mail.

That's my rule:

{"rules_svds_send_mail_to_product_owner": {
"LABEL": "SVDS: Send an email to the product owner",
"PLUGIN": "reaction rule",
"ACTIVE": false,
"OWNER": "rules",
"KEYWORDS" : [ "SVDS" ],
"REQUIRES" : [ "rules", "commerce_payment" ],
"ON": {"commerce_payment_order_paid_in_full": [] }
"MAKE" : [
  { "variable_add" : {
      "USING" : { "type" : "commerce_order", "value" : [ "commerce-order" ] }
"PROVIDE": {"variable_added": {"commerce_order_value": "Order of Commerce"}}
}
}
{"LOOP": {
"USING": {"list": [ "commerce-order:commerce-line-items" ] }
"ITEM": {"line_items": "Trade Line Items"},
"MAKE" : [
        { "component_rules_perform_an_action_on_a_selected_line_item" : { "selected_line_item" : [ "line-items" ] }}
]}
}
]}
}

The component I use in the loop looks like this:

{"rules_perform_an_action_on_a_selected_line_item": {
"LABEL": "Perform an action on a selected line item",
"PLUGIN": "rule",
"OWNER": "rules",
"REQUIRES" : [ "rules", "mimemail" ],
"VARIABLE USES": {
"selected_line_item": {"label": "Selected line item", "type": "commerce_line_item"},
"commerce_order": {"label": "Trade Order", "type": "trade_order"}
}
"IF" : [
  { "entity_has_field" : { "entity" : [ "selected-line-item" ], "field": "commerce_product"}}
],
"MAKE" : [
  { "entity_fetch" : {
      "USING" : {
        "type" : "commerce_product",
        "id" : [ "selected-line-item:commerce-product:product-id" ]
      }
"PROVIDE": {"entity_fetched": {"product_fetched": "Product recovered"}}
}
}
{"entity_fetch": {
"USING": {"type": "commerce_order", "id": [ "commerce-order:order-id" ] }
"PROVIDE": {"entity_fetched": {"fetched_customer": "Recovered user"}}
}
}
{"mimemail": {
"USING": {
"key": "[commerce-order:order-id]"
"at" : "[product-fetched:field-e-mailadres-product]"
"subject": "Product ordered",
"body": "E-mail body text",
"language" : [ "" ]
      }
"PROVIDE": {"send_status": {"send_status": "Send Status"}}
}
}
]}}

Thanks in advance