Bug 153412 Change parameter type will cause preview fail
Description: Change parameter type will cause preview fail Steps to reproduce: 1. New a report paramter, string, text-box, default value is abc. 2. Drag the parameter to Layout and preview. 3. Change the parameter's type to integer, list-box, add a value 1 4. Preview Expected result: No errors. Actual result: The value "abc" is invalid with the type "integer".
viewer/org.eclipse.birt.report.viewer/birt/WEB-INF/classes/org/eclipse/birt/report/context/ViewerAttributeBean.java
this.missingParameter = false;
		else
			this.missingParameter = validateParameters( parameterDefList,
					this.parametersAsString );
		
		this.parametersAsString = getParsedParametersAsStringWithDefaultValue(
				this.parametersAsString, request, options );
		
		this.parameters = (HashMap) getParsedParameters(
				this.reportDesignHandle, parameterList, request, options );
		
		this.displayTexts = getDisplayTexts( this.displayTexts, request );
	}
	/**
	 * parse paramenters from config file.
	 * 
	 * @param request
	 *            HttpServletRequest
	 * @return
	 */
	protected void parseConfigVars( HttpServletRequest request,
			Collection parameterList )
	{
		this.configMap = new HashMap( );
		
		String reportConfigName = ParameterAccessor
				.getConfigFileName( this.reportDesignName );
		if ( reportConfigName == null )
			return;