Getting this error for the below apex test class: 

Apex Handler: 
public class InsertIncomeRecordHandler {
    public static void insertRecord(List<Salary_Detail__c> salList,Map<id,Salary_Detail__c> oldMap){
        Set<Id> empId = new Set<Id>();
        List<D_Transaction__c> dList = new List<D_Transaction__c>();
        ID income = Schema.SObjectType.D_Transaction__c.getRecordTypeInfosByName().get('Income').getRecordTypeId();
        ID trans = Schema.SObjectType.Salary_Detail__c.getRecordTypeInfosByName().get('Transaction').getRecordTypeId();
        ID expense = Schema.SObjectType.D_Transaction__c.getRecordTypeInfosByName().get('Expense').getRecordTypeId();
        
        for(Salary_Detail__c sd : salList){
            if(sd.Advance__c != oldMap.get(sd.Id).Advance__c && sd.Isdetected__c !=oldMap.get(sd.Id).Isdetected__c){
            if(sd.Advance__c >0 && sd.RecordTypeId == trans && sd.Organization__c == 'Deshkal'){
                empId.add(sd.Employee_Information__c);
            }
            }
            
            system.debug(' empIdt' + empId);
        }
        
      
        for(Employee_Information__c emp : [select id,Name From Employee_Information__c where id IN :empId]){
        for(D_Transaction__c dt : [SELECT RecordTypeId,D_Amount__c,D_Employee__c,D_Advance_Status__c,D_Advance_Repay__c,D_Name__c FROM D_Transaction__c where D_Employee__c =:emp.Id AND RecordTypeId =:expense AND D_Advance_Status__c = 'Open' ]){
            
                D_Transaction__c d = new D_Transaction__c();
                d.D_Employee__c = emp.Id;
                d.RecordTypeId = income;
                d.D_Transaction__c =dt.Id;
                Integer result = integer.valueOf(dt.D_Amount__c) / integer.valueOf(dt.D_Advance_Repay__c);
                d.D_Amount__c = result;
                system.debug('d.D_Amount__c');
                dList.add(d);
            
        }
        }
        
        if(!dList.isEmpty()){
            insert dList;
        }
    }
}


Test Class:
@isTest
private class InsertIncomeRecordHandlerTest {

    @isTest
    static void testInsertRecord() {
        // Create test data
        Employee_Information__c emp = new Employee_Information__c();
        emp.Salutation__c = 'Mr.';
        emp.Name = 'Test';
        emp.Employee_Last_Name__c = 'HR Admin';
        emp.Date_of_Join__c = system.today();
        emp.Gender__c = 'Male';
        emp.Personal_Email__c = 'abc@gmail.com';
        emp.Marital_Status__c = 'Single';
        emp.Employment_Status__c = 'Active';
        emp.DN_Designation__c='CEO';
        emp.Date_of_Birth__c=Date.newInstance(2000, 12, 9);
        emp.Gender__c='Male';
        emp.Manager_Supervisor__c = 'Deepu H D';
        emp.Work_Location__c = 'NOC';
        emp.Bank_Name__c='HDFC';
        emp.Account_Number__c='12345678901234';
        emp.Mobile_Number__c='9999999999';
        emp.IFSC_CODE__c='HDFC0000003';
        emp.Confirmed_CTC__c=800000;
        emp.Basic_Percentage__c='40';
        emp.Tax_Regime__c='Old Regime';
       emp.PFs__c='Percentage';
        emp.Marital_Status__c='Single';
        emp.Aadhaar_Number__c='265385644663';
        emp.Address__c='Test';
        emp.City__c='Chennai';
       emp.Organization__c='Deshkal';
        emp.Postal_Code__c='600001';
      emp.DN_Leave_Process__c='Yes';
        insert emp;

        Salary_Detail__c salary = new Salary_Detail__c(
            Employee_Information__c = emp.Id,
            RecordTypeId = Schema.SObjectType.Salary_Detail__c.getRecordTypeInfosByName().get('Transaction').getRecordTypeId(),
            Advance__c = 60,
            Isdetected__c = false,
            Organization__c = 'Deshkal'
        );
        insert salary;

        
      D_Transaction__c dt = new D_Transaction__c ();
             dt.D_Employee__c = emp.Id;
        dt.D_Amount__c = 100;
            dt.D_Advance_Repay__c =' 12';
            dt.RecordTypeId = Schema.SObjectType.Salary_Detail__c.getRecordTypeInfosByName().get('expense').getRecordTypeId();
        dt.D_Advance_Status__c = 'Open';
                
                               
                     

       
        Test.startTest();
insert dt;
        Test.stopTest();
        
      }
        



}