validation while linking an issue based custom fields value?

[Suresh]

I am trying following validation.

While linking an issue, The current issue custom-field value and linking issue custom-field value matches then allow to link at least once. And also check in already linked issues if the match there then skip the validation.
It required at least on association and if not show validation message.

" When Cause field value is 'Product Feature' then require at least one 'Issue Link' with relationship of "is caused by" must exist and must have a linked GTN Epic of where the Epic's 'Feature Type' field has the value of 'Product Feature'. _Message:_ "'Product Feature' Cause requires at least one 'is caused by' issue link relationship to a 'Product Feature' Epic.  "

If the match is already linked issue, then skip the validation, 

def linkManager = ComponentAccessor.issueLinkManager

def issueManager = ComponentAccessor.getIssueManager()
def customFieldManager = ComponentAccessor.getCustomFieldManager()
def cField = customFieldManager.getCustomFieldObject("customfield_18813")//Cause Field
def featureType = customFieldManager.getCustomFieldObjectByName("Feature Type")//FeatureType Field
def cFieldValue = issue.getCustomFieldValue(cField)

def fieldManager = ComponentAccessor.getFieldManager()
def linksSystemField = fieldManager.getField("issuelinks") as IssueLinksSystemField
def request = ActionContext.getRequest()
   
if (request) {          
         def params = request.getParameterMap()             
         def issueLinkingValue = linksSystemField.getRelevantParams(params) as IssueLinksSystemField.IssueLinkingValue      
         if("Product Feature" in cFieldValue.collect{it.toString()}){
               linkManager.getOutwardLinks(issue.id).each{
                 def linkedIssue = it.destinationObject
                 def featureTypeValue = linkedIssue.getCustomFieldValue(featureType)
                 if(featureTypeValue.toString() == "Product Feature"){
                 for (link in issueLinkingValue.linkedIssues){
                 def object=ComponentAccessor.getIssueManager().getIssueObject(link)
                 if(object.getCustomFieldValue(featureType).toString() != "Product Feature"){          
                 throw new InvalidInputException(IssueFieldConstants.ISSUE_LINKS,
                  "Note: "'Product Feature' Cause requires at least one 'is caused by' issue link relationship to a 'Product Feature' Epic.")          
                }
               }
              }
             }
           } 
      }