[birt-dev]CheckIn: when execute subquery, we should return null if the p

["Wei Zhao \(Shang\)" <wei.zhao@xxxxxxxxxxx>]

Title: [birt-dev]CheckIn: when execute subquery, we should return null if the parent resultSet is null

- Summary:
When execute subquery, we should return null if the parent resultSet is null instead of throw NPE.

- Bugzilla Bug (s) Resolved:
NONE

- Description:
When execute subquery, we should return null if the parent resultSet is null instead of throw NPE.

- Tests Description  :
Manual Test.

- Notes to Build Team:

- Notes to Developers:

- Notes to QA:  
 
- Notes to Documentation:  

- Files Edited:
"/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/data/dte/AbstractDataEngine.java"

- Files Added:

- Files Deleted

-Wei Zhao(Shanghai)