invalid ID error using SOQL to get field from related record

Question

I am getting an invalid ID error in my VF page on the below code and I don't understand what I am missing.

In my controller's constructor I am running the below code:

system.debug('SystemChangeRequest View/Edit PAGE demand ID: '+sObjectRFC.Demand__c);

system.debug('SystemChangeRequest View/Edit PAGE GET DEMAND QRY');
if (sObjectRFC.Status__c=='Converted' && sObjectRFC.Demand__c !=''){
    system.debug('SystemChangeRequest View/Edit PAGE GET DEMAND inside IF block');
    demandName=[Select Id, Name from apm2__Demand__c where Id =: sObjectRFC.Demand__c].Name;
    system.debug('SystemChangeRequest View/Edit PAGE demand ID: '+sObjectRFC.Demand__c);

    //demandName='TEST DEMAND';
} 

in the developer console logs I can see that sObjectRFC.Demand__c = 'a0U8E000002tZwj'

and I can access that record on the Demand object through salesforce with the url https://domain.salesforce.com/a0U8E000002tZwj

Of course I can show the Id in my VF page with no problems, but I want to show the record identifier which looks like this: D-04235

In the Demand object, the field is defined as:

Now, in the developer console I can write the below SOQL query:

Select Name, Id from apm2__Demand__c where Id ='a0U8E000002tZwj'

and it returns a record with the results as below:

In my VF page, I want to show the Name field from the demand object, which should be D-04235

but the when I run my VF page, all I can see in the log (developer console) is:

so it just stops with that error after the line system.debug('SystemChangeRequest View/Edit PAGE GET DEMAND QRY');

so what am I doing wrong?

Answer 1

Id fields cannot be compared with the '' value. If you need to check for blank , then use "null" instead of ''. So change your check like this :

system.debug('SystemChangeRequest View/Edit PAGE demand ID: '+sObjectRFC.Demand__c);

system.debug('SystemChangeRequest View/Edit PAGE GET DEMAND QRY');
if (sObjectRFC.Status__c=='Converted' && sObjectRFC.Demand__c != null){
    system.debug('SystemChangeRequest View/Edit PAGE GET DEMAND inside IF block');
    demandName=[Select Id, Name from apm2__Demand__c where Id =: sObjectRFC.Demand__c].Name;
    system.debug('SystemChangeRequest View/Edit PAGE demand ID: '+sObjectRFC.Demand__c);

    //demandName='TEST DEMAND';
}