How can i get the value of a insight custom field using Scriptrunner behavior, and write this fields value into the summary field?
Environment: Datacenter
This is my custom field inside service portal:

And i want to get the value of the "Use old Project to pre-fill fields" field. This value should be written inside the "Summary" field.
However, every approach which I have found online and tested, unfortunately does not want to work.
This is my code:
1. Attempt
import com.atlassian.jira.component.ComponentAccessor
import com.atlassian.jira.issue.CustomFieldManager
import com.atlassian.jira.issue.MutableIssue;
import com.atlassian.jira.issue.fields.CustomField
def summary = getFieldById("summary")
def useProjectToFill = getFieldById("Use old Project to pre-fill fields")
String selectedProj = useProjectToFill.getFormValue().toString()
if (summary.getFormValue() == null || summary.getFormValue().toString().length() < 1) {
summary.setFormValue("nothing selected")
} else {
summary.setFormValue(selectedProj)
}
Result:
Nothing selected so far so okay ->

Project select ... Not so okay... ->

2. Attempt
import com.atlassian.jira.component.ComponentAccessor
import com.atlassian.jira.issue.CustomFieldManager
import com.atlassian.jira.issue.MutableIssue;
import com.atlassian.jira.issue.fields.CustomField
def field = ComponentAccessor.getCustomFieldManager().getCustomFieldObject("Use old Project to pre-fill fields")
def value = underlyingIssue.getCustomFieldValue(field)
def summary = getFieldById("summary")
String useProjectToFill = getFieldById("Use old Project to pre-fill fields").getFormValue().toString();
if (summary.getFormValue() == null) {
summary.setFormValue("nothing selected")
} else {
summary.setFormValue(useProjectToFill)
}
This attempt breaks the behavior and summary is empty all time.
Pls help