title: Roll up field for currency datatype fields is not working for custom entities
body: <p>Following is the exact scenario in my Dynamics CRM instance.</p>
  
  <p>I have created a custom entity (say, Order), which is having a lookup field (say, Item). The lookup field is pointing to another entity which is having a currency field (say, Amount). I have created a roll-up field (say, Total Amount) in Order entity, and set it to calculate sum of Amount for all items for the order. Once created, I have placed the control on main form of the entity.</p>
  
  <p>When I try to check the value of rollup field (by clicking Refresh icon of the roll-up field), it gives me following error:</p>
  
  <blockquote>
    <p>Record currency is required to calculate rollup field of type
    currency. Provide a currency and try again.</p>
  </blockquote>
  
  <p>I tried similar for Account and Opportunities entities, and the new rollup field works perfectly there.</p>
  
  <p>Any idea why it doesn't work for the custom entity? Do I need to do anything extra at entity or form level?</p>