A script field that displays issues where the current issue is selected in Issue Picker fields

import com.atlassian.jira.bc.issue.search.SearchService
import com.atlassian.jira.component.ComponentAccessor
import com.atlassian.jira.jql.builder.JqlQueryBuilder
import com.atlassian.jira.web.bean.PagerFilter
import com.atlassian.query.operator.Operator

def searchService = ComponentAccessor.getComponent(SearchService)
def loggedInUser = ComponentAccessor.jiraAuthenticationContext.getLoggedInUser()

// Modify the name of your issue picker field here
def issuePickerFieldName = 'Root Cause'

// This creates a query like: "issueFunction in issuePickerField('Root Cause', 'key = ${issue.key}')"
// You could also use JqlQueryParser.
def query = JqlQueryBuilder.newClauseBuilder().addFunctionCondition(
    'issueFunction',
    Operator.IN,
    'issuePickerField',
    issuePickerFieldName,
    "key = ${issue.key}"
).buildQuery()

def searchResults = searchService.search(loggedInUser, query, new PagerFilter(1000))

searchResults.results ?: null