Bug 135490 Error occurs when Preview Results of Inner Join datasets
Description: Create a sample datasource and dataset, and then create a Joint dataset. Error occurs when preview results in the data set dialog. Steps to reproduce: 1.Create a sample datasource, and a dataset with sql statement "select * from CLASSICMODELS.CUSTOMERS". 2.Create a Joint dataset, the left and right dataset is the same. 3.Preview result in the dataset dialog, error pops up continuely.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/jointdataset/JoinConditionMatchUnit.java
private Scriptable scope = null;
	private boolean isColumnReference = false;
	
	/**
	 * Constructor 
	 * 
	 * @param ri
	 * @param columnName
	 */
	public JoinConditionMatchUnit( IResultIterator ri, String columnName )
	{
		this.columnName = columnName;
		this.ri = ri;
		this.isColumnReference = true;
	}
	
	/**
	 * Constructor
	 * 
	 * @param expr
	 * @param scope
	 */
	public JoinConditionMatchUnit( IScriptExpression expr, Scriptable scope )
	{
		this.expr = expr;
		this.scope = scope;
		this.isColumnReference = false;
	}
	
	/**