"Show parent issue in hierarchy" Script Field breaks when target issue has a parent

When using the "Show parent issue in hierarchy" built-in Script Field, if your target parent issue has a parent of its own then the field will fail to populate on all of the target issue's children. 

Steps to Reproduce:

1. Set up a basic project
2. Go to the Script Fields configuration page and add a new "Sho parent issue in hierarchy" field with the following config:

1. 1. Field Name: Bug Link
   2. Field Description: ----
   3. Field Note: ----
   4. Target Issue Type: Bug
   5. Parent Navigators: "Links: Blocks"
2. Create two issues, one of issue-type Bug and the other of issue-type Task
3. Link the Task to the Bug with an "is blocked by" link and notice that the Script Field appears on the Task with the key of the Bug.
4. Now create another issue with the issue-type New Feature
5. Link your Bug to the New Feature type issue that you've just created with an "is blocked by" link.
6. Navigate back to the Task issue that you created on step 3 and notice that the "Bug Link" field is no longer present on the ticket.