I have a page that is giving the user the option to add line items to a catalog order. I'm able to display the catalog items, my debug code is showing that the setter is getting the integer entered into the input field, but either no line items get added or all items are added, not just the ones that have a value entered in the field.  I'm not seeing the issue and am hoping that the community sees something I"m missing. 

Here is my controller: 

public with sharing class selectableProduct {

    public Material_Order__c record;
    public Integer amount{get; set;}
    public Product_vod__c prod{get;set;}
    public List<Product_vod__c> productList=new List<Product_vod__c>();
    public List<Material_Order_Line_Item__c> linesToAdd=new List<Material_Order_Line_Item__c>();

    //set current material order in focus
    public selectableProduct(ApexPages.StandardController stdController){
        record = [SELECT id, Name, Date__c, Status__c, Notes__c
                    FROM Material_Order__c 
                    WHERE id =:ApexPages.currentPage().getParameters().get('id')];

    }
    
    //get list of available products to order
    public List<Product_vod__c> getProductList(){
        productList = [SELECT id, Name, Image__c FROM Product_vod__c WHERE Product_Type_vod__c = 'Order' ORDER BY Name ASC];
        return productList;
    }
    
    public Integer getAmount(){
        return amount;
      }
   public void setAmount(Integer a){
       this.amount = a;
       }
    
    //set amounts of selected items and insert line items on material order
    public pageReference placeOrder(){
    
        pageReference orderQtys = new PageReference('/'+record.id);
 
        for(Product_vod__c ps : productList){

            Material_Order_Line_Item__c newLine = new Material_Order_Line_Item__c();
          
           if((amount != NULL) || (amount != 0)){
            newLine.Products__c = ps.id;
            newLine.Quantity__c = amount;
            newLine.Material_Order__c = record.id;

            linesToAdd.add(newLine);
            }
        }
        insert linesToAdd;
        return orderQtys;
    }
    
}

And here is the VF Code: 

<apex:page standardController="Material_Order__c" extensions="selectableProduct">
<apex:form >
<apex:pageBlock title="Products">
  <apex:pageBlockButtons >
    <apex:commandButton action="{!placeOrder}" value="Submit"/>
  </apex:pageBlockButtons>
<apex:pageBlockSection title="Available Line Items" columns="1">
  <apex:dataTable value="{!productList}"  var="prod" width="95%" cellpadding="5">
    <apex:column width="10%" headerValue="Amount">
      <apex:facet name="header"/>
      <apex:inputText value="{!amount}"/>
    </apex:column>
    <apex:column width="20%">
      <apex:facet name="header">Product</apex:facet>
      <apex:outputText value="{!prod.Name}"/>
    </apex:column>
    <apex:column width="70%">
      <apex:facet name="header">Image</apex:facet>
      <apex:outputField value="{!prod.Image__c}"/>
    </apex:column>
  </apex:dataTable>
</apex:pageBlockSection>
</apex:pageBlock>
</apex:form>
</apex:page>

Thanks for your help in advance!

JoAnn