1.Create quote button from opportunity page (detail page) is giving the below error when clicked.
  This custom button is calling URL /apex/ManageQuote/ apex code but its giving error

Error
--System.NullPointerException: Attempt to dereference a null object line 31 column 1 which is under public PageReference createQuote() of ManageQuoteController code.

can let us know what is the issue?Thanks in advance for help

Code snippet:
---ManageQuoteController code:
public with sharing class ManageQuoteController {
    //Opportunity Reference
    public Opportunity opportunityRef {get; set;}
    //Quote Creation Error
    public Boolean quoteCreationError {get; set;}
    //Quote created indicator
    public Boolean quoteCreated {get; set;}
    //Error Message
    public String errorMessage {get; set;}
    //Quote URL
    public String quoteUrl {get; set;}
    //Default Controller
    public ManageQuoteController() {
        quoteCreated = false;
        quoteCreationError = false;
        Id opptyId = ApexPages.currentPage().getParameters().get('opportunity.id');
        try{
        opportunityRef = [select Id, Name from Opportunity where Id = :opptyId];
        }
        catch (System.QueryException e) {
          System.debug('caught ya!');
        }
    }
   
    public PageReference goback() {
        return new Apexpages.Standardcontroller(opportunityRef).view();
    }
   
    public PageReference createQuote() {
        Opportunity oppty = [select Id, Name, StageName, CloseDate, Owner.Name, AccountId, Account.Name,
            Account.Sic, Account.Industry, Account.BillingStreet, Account.BillingCity, Account.BillingState,
            Account.BillingPostalCode, Account.BillingCountry from Opportunity where Id = :opportunityRef.Id];
        OpportunityContactRole ocr = [select Contact.FirstName, Contact.LastName, Contact.EMail, Contact.Phone, Contact.Fax
            from OpportunityContactRole where opportunityId = :opportunityRef.Id and IsPrimary = true];
        QuoteResponse response = QuoteServiceDelegate.createQuote(oppty, ocr.Contact);
        if (response.stausCode != 200) {
            quoteCreationError = true;
            errorMessage = response.message;
        } else {
            quoteCreated = true;
            quoteUrl = response.quoteUrl;
        }
        return null;
    }
}



---Manage Quote code

<apex:page name="ManageQuote" controller="ManageQuoteController" id="thisPage" tabStyle="Opportunity">
        <script type="text/javascript">
                function init() {
                        if ('{!quoteCreationError}' == 'false' && '{!quoteCreated}' == 'false')
                                createQuote();
                }
                window.onload = init;
    </script>
        <apex:form >
                <apex:actionFunction name="createQuote" action="{!createQuote}"  rerender="outputBlock, quoteBlock" status="createStatus" />
                <apex:sectionHeader title="Manage Quote" subtitle="{!opportunityRef.Name}"/>
                <apex:outputPanel id="outputBlock">
                        <apex:actionStatus id="createStatus">
                                <apex:facet name="start">
                                        <apex:pageBlock >
                                                <apex:outputText >Creating quote. Please wait...</apex:outputText>
                                        </apex:pageBlock>
                                </apex:facet>
                        </apex:actionStatus>
                </apex:outputPanel>
                <apex:outputPanel id="quoteBlock">
                        <apex:pageBlock id="errorBlock" title="Error" rendered="{!quoteCreationError}">
                                <apex:pageBlockButtons location="bottom">
                                        <apex:commandButton value="Go Back" action="{!goback}" />
                                </apex:pageBlockButtons>
                                <apex:pageBlockSection columns="1">
                                        <apex:outputText value="{!errorMessage}"/>
                                </apex:pageBlockSection>
                        </apex:pageBlock>
                        <apex:iframe src="{!quoteUrl}" scrolling="true" id="quoteFrame" rendered="{!quoteCreated}"/>
                </apex:outputPanel>
        </apex:form>
</apex:page>