Good day I am encountering the error below:

   'LeadStandardController.customerName'
Basically I want to upload a record that has already been created.
Please find below my code:

**VF Page**	

    <apex:page tabStyle="Account" standardController="Lead" extensions="CIFController" docType="html-5.0" showHeader="false" sidebar="false">
	<apex:form>
		<ul>
			<apex:outputPanel layout="block">
			<apex:pageBlock >
			<apex:outputPanel > 
				<apex:pageblocksection title="MAIN CONTACT DETAILS: INDIVIDUAL CONNECTED WITH THIS APPLICATION" collapsible="false"  >
					<apex:inputTextArea value="{!Customer_Name__c}" required="true" html-placeholder="Customer Name:"/>
					<apex:inputTextArea value="{!Licence_c}" required="true" html-placeholder="Licences - if any:"/>      
					<apex:inputTextArea value="{!Email_c}" required="true" html-placeholder="Email"/>
					<apex:inputTextArea value="{!Surname_and_First_Name__c}" required="true" html-placeholder="Surname and Name"/>
					<apex:inputTextArea value="{!Job_Title__c}" required="true" html-placeholder="Job Title"/>           
					<apex:inputTextArea value="{!Telephone_Number__c}" required="true" html-placeholder="Telephone Number"/> 
				</apex:pageblocksection>
				<apex:pageblocksection >
					<apex:inputTextArea value="{!Business_Profile__c}" required="true" html-placeholder="Business Profile:"/> 
				</apex:pageblocksection>			
				<apex:outputPanel >
						  <p style="color:#629DD1;font-family:Fauna One"><b>Attach a copy of the business letterhead and the identification document of the customer representative.</b></p>       
				</apex:outputPanel> 
				<apex:pageblocksection title="BUSINESS REGISTRATION & ID CARD STATUTORY DOCUMENTS" collapsible="false">  
				  <apex:inputFile title="Identity Card" style="width:100%" id="fileToUpload1" value="{!idCardBody }" filename="{!idCardName }" />      
				  <apex:inputFile title="Business Registration Document" style="width:100%" id="fileToUpload" value="{!documentBody }" filename="{!businessDocName }" /> 
				</apex:pageblocksection>
				</apex:outputPanel> 
				<apex:pageBlock >
				  <apex:commandButton styleClass="submit" value="Submit    Application" action="{!UpdateRecord}"/>
				</apex:pageBlock>
			</apex:pageBlock>
			</apex:outputPanel>
		</ul>
	</apex:form>
</apex:page>

**Apex Extension**

      public class CIFController
      {
       public Lead leadDetail 
       {get;set;}
       public Id leadId
       {get;set;}
	   //attachment Document name
       public string businessDocName 
       {get;set;}
      //attachment Document body
      public Blob documentBody 
      {get;set;} 
      //attachment ID name
      public string idCardName 
      {get;set;}
      //attachment ID body
      public Blob idCardBody 
      {get;set;} 
      //get the lead id record
      public CIFController(ApexPages.StandardController ctlr)
      {
         leadId = ctlr.getRecord().Id;     
      }
      //update the fields on the record 
      public PageReference UpdateRecord(){
          Id leadId ;
          //lead custom fields and definitions 
          leadDetail = [SELECT Customer_Name__c, Licence_c, Email_c, Surname_and_First_Name__c, Job_Title__c, Telephone_Number__c FROM Lead WHERE Id  =: leadid];
 
          PageReference pgRef;
          if((documentBody != null && businessDocName != null)||(idCardBody !=   null && idCardName != null))
          {
              Attachment businessDocument  = new Attachment();
              Attachment idDocument  = new Attachment();
               if(documentBody != null && businessDocName != null)
              {
                  businessDocument.Body = documentBody;
                  businessDocument.Name = businessDocName;
                  businessDocument.ParentId = leadId;
                  try
                 {
                      if(idCardBody != null && idCardName != null)
                      { 
                          idDocument.Body = idCardBody;
                          idDocument.Name = idCardName;
                          idDocument.ParentId = leadId;
                      }
                      insert businessDocument;
                      insert idDocument;
                  }catch(DMLException e)
                  {
                      ApexPages.addMessage(new   ApexPages.message(ApexPages.severity.ERROR,'Error uploading attachment'));
                          return null;
                  }
              }
              pgRef = new PageReference('http://thank.you/');
              pgRef.setRedirect(true);
              return pgRef;
          }   
          return null;
      }    
  }

How can I fix it? Thank you in advance for the suggestions and assistance...