Apex Inputtext not getting assigned to variable in apex controller

I have below pageblocksectionitem in VF Page.

 <apex:pageBlockSection showHeader="false" columns="2" id="blockseciframe" >
                <apex:pageBlockSectionItem >

      <apex:outputLabel value="Survey Name"/>
      <apex:inputText value="{!Survey}" id="SurveyName"/>
     </apex:pageBlockSectionItem>

     <apex:pageBlockSectionItem >

I have simply put getter and setter for the variable Survey in my with sharing class controller.

public String Survey{get;set;}

Unfortunately when I try accessing it from a pagereference method, it prints null in system debug log.

I am having apex form here. Please find the whole of controller snippet here.

public Attachment attachment {
    get {
    if (attachment == null)
    attachment = new Attachment();
    return attachment;
    }
    set;
}

public Survey__c SurveyApproval{
    get {
    if (SurveyApproval == null)
    SurveyApproval = new Survey__c ();
    return SurveyApproval;
    }
    set;
}

public PageReference upload() {

    SurveyApproval.Name = attachment.Name;
   system.debug('Survey@' + Survey);
   system.debug('Description@' + Description);
   system.debug('selectedStatus@' + selectedStatus);
    SurveyApproval.SurveyName__c = Survey;
    attachment.Description = Description;
    SurveyApproval.Approval__c = selectedStatus;

    SurveyApproval.ApprovalBy__c = UserInfo.getUserId();

    system.debug('SurveyApproval@' + SurveyApproval);
    attachment.OwnerId = UserInfo.getUserId();

    attachment.IsPrivate = true;
    attachment.ContentType = 'text/csv';
    List<Survey__c> insertList = new List<Survey__c>();
    insertList.add(SurveyApproval);
    system.debug('insertList@' + insertList);

    if(SurveyApproval.Id==null && attachment.body!=null)
    {Database.SaveResult[] srList = Database.insert(insertList);

        for (Database.SaveResult sr : srList)
        {
            ApprovalSurveyId = sr.getId();
        }
    }



    attachment.ParentId = ApprovalSurveyId ;
      system.debug('attachment@' + attachment);
    try {

      insert attachment;
    } catch (DMLException e) {
      ApexPages.addMessage(new ApexPages.message(ApexPages.severity.ERROR,'Error uploading attachment'));
      return null;
    } finally {
      attachment = new Attachment(); 
    }

    ApexPages.addMessage(new ApexPages.message(ApexPages.severity.INFO,'Attachment uploaded successfully'));
PageReference p = Apexpages.currentPage(); 
        p.setRedirect(false);
        return null; 

}

Can someone help me please?