why it is showing Formula Expression is required on the action attributes

Question

<apex:page controller="c1" showHeader="false" sidebar="false">
<apex:form>

<apex:pageBlock>
<apex:pageBlockSection title="Login page">
<apex:inputText label="Name" title="Name" value="{!Name}"/>
<apex:inputText label="Ucode" title="Ucode" value="{!Ucode}"/>

</apex:pageBlockSection>
<apex:commandButton value="Dep" action='{!Dep}'/>

</apex:pageBlock>
</apex:form>

</apex:page>

---

public class c1 {
    public string Name{set;get;}
    public string Ucode{set;get;}
    PageReference P1;

    public PageReference Dep() {
    Employee__c obj;

   obj=[select Emp_Name__c,Ucode__c from Employee__c where Emp_Name__c='Saurabh' AND Ucode__c='MG356'];

    if(obj!=null){
       P1 =new PageReference('www.google.com/');
     }
    else {
       P1 =new PageReference('https://mail.google.com/mail/u/0/#inbox');    
     }
   return P1;
   }
}

Why it is showing this error?

Formula Expression is required on the action attributes

Answer 1

The code exactly as posted (with the duplicate markup removed, the custom object query commented out but with the uncommon single quotes left in) compiles and runs fine in a scratch org of mine. If this code is a cut down version, then the problem probably lies in the code you have not included. If this is the exact code, cut and paste it from here into your org.

To echo David Reed's point, the clearer your code and question are, the better the chances of a good answer so ensure e.g. the indenting is good when you post code or page markup.

Answer 2

change this

P1 =new PageReference('www.google.com');

To this

P1 =new PageReference('https://www.google.com');