Bug 161191 Null is inserted when drag columns to query text with ctrl key pressed
Description: Null is inserted when drag columns to query text with ctrl key pressed Steps to reproduce: 1. New a data source. 2. New a dataset. 3. Press and hold ctrl key, select OFFICECODE and CITY columns, drag to query text. Expected result: "CLASSICMODELS.OFFICES.OFFICECODE,CLASSICMODELS.OFFICES.CITY" is inserted in query text. Actual result: "null,CLASSICMODELS.OFFICES.OFFICECODE,CLASSICMODELS.OFFICES.CITY" is inserted
data/org.eclipse.birt.report.data.oda.jdbc.ui/src/org/eclipse/birt/report/data/oda/jdbc/ui/editors/SQLDataSetEditorPage.java
DbObject schemaObj = new DbObject( schemaName,
								schemaName,
								DbObject.SCHEMA_TYPE,
								schemaImage );
						schemaObjectList.add( schemaObj );
						count++;
					}
				}
			}
			else
			{
				String schemaName = schemaCombo.getItem( schemaCombo.getSelectionIndex( ) );
				DbObject schemaObj = new DbObject( schemaName,
						schemaName,
						DbObject.SCHEMA_TYPE,
						schemaImage );
				schemaObjectList.add( schemaObj );
			}
			TreeItem[] items = Utility.createTreeItems( rootNode,
					schemaObjectList,
					SWT.NONE,
					schemaImage );
			if ( items != null && items.length > 0 )
			{
				availableDbObjectsTree.showItem( items[0] );
			}
		}
	}
	
	/**