I have the following Apex class that is only getting 57% code coverage.  Test class below as well. I feel like there is something simple that I'm missing. Any help would be appreciated!

public class taskController{

    public Project_Task__c task{get;set;}
    public List<Project_Task_Assignment__c> assignment{get;set;}
    public taskController(){
        task = new Project_Task__c();
        assignment = new List<Project_Task_Assignment__c>();
        task.Project__c = ApexPages.currentPage().getParameters().get('Id');
     
    }
    public void AddRow(){
        assignment.add(new Project_Task_Assignment__c());
    
    }
    public PageReference save(){

     try{
            insert task;
            List<Project_Task_Assignment__c> taskAssignment = new List<Project_Task_Assignment__c>();
            for(Project_Task_Assignment__c c : assignment){
                c.Project_Task__c = task.id;
                taskAssignment.add(c);
    
            }

            if(assignment != null){
                insert taskAssignment;
           }
           
            PageReference taskPage = new PageReference('/apex/manage_task?id=' + task.id);
        taskPage.setRedirect(true);
        return taskPage;
      } 
      
     catch (Exception e) {apexpages.addmessages(e);}return null;        
      
  }  
    
}

*****Test Class*****
@isTest
    public class taskControllerTest{
         private static testMethod void saveTask() {
        
         Account acc = new Account(Name = 'Sample Account'); insert acc;
         Contact con = new Contact(LastName = 'Smith', AccountId = acc.id); insert con;    
         Plan__c plan = new Plan__c(Name = 'Test'); insert plan;
         Project__c project = new Project__c(Name = 'Test', Plan__c = plan.id); insert project;
         
    
            
    
         Test.startTest();
         
         PageReference pageRef = Page.AccountContact;
         
         Project_Task__c task = new Project_Task__c(Project__c = project.id, Name = 'Test Task'); 
         insert task;
         Project_Task_Assignment__c assignment = new Project_Task_Assignment__c(Project_Task__c = task.id, Contact__c = con.id);
         insert assignment;
         Test.setCurrentPage(pageRef);
         taskController controller = new taskController();
         controller.addRow();       

         controller.save();
         pageRef.getParameters().put('id',task.id);   

         Test.stopTest();        
         
         System.assertNotEquals(task.Name, null);
         System.assertNotEquals(assignment, null);         
    
   } 
             
}