Bug 164764 Joint data set does not work properly using attached flatfile
The data set preview keep empty in joint data set. Step to reproduce: 1.Create two data sets based on attached flat file 2.Make an inner join using joint data set with key "A". 3.Preview data set in data set editor. Expect result: The data set preview correctly Actual result: The data set preview is empty.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/script/ScriptEvalUtil.java
/**
	 * @param exprText
	 * @param value
	 * @return an instance of ExprTextAndValue
	 */
	public static ExprTextAndValue newExprInfo( String exprText, Object value )
	{
		return ExprTextAndValue.newInstance( exprText, value );
	}
	
	/**
	 * Evaluates a conditional expression. A conditional expression comprises of
	 * a Javascript expression, an operator, and up to 2 operands (which are
	 * Javascript expressions themselves).<br>
	 * Both op1 and op2 will be encapsulated to ExprTextAndValue type to show
	 * specific message in case anything goes wrong, they are assumed not to be
	 * null as well.
	 * <p>
	 * The basic rule for comparison: obj will always be considered as the
	 * default data type,i.e. obj, op1 and op2 will be formatted to the superset
	 * of obj (or Double if obj is numeric)on the condition they are comparable.<br>
	 * e.g.<br>
	 * obj: Integer=>obj, op1 and op2 will be formatted to Double.<br>
	 * obj: Timestamp=>obj, op1 and op2 will be formatted to Date.<br>
	 * obj: Boolean=>obj and op1 will be formatted to Boolean.<br>
	 * obj: String=>obj, op1 and op2 will remain the same
	 * 
	 * @param obj
	 * @param operator
	 * @param op1