Bug 161501 [Smoke] Chart can not be previewed in Web Viewer & HTML
Chart can not be previewed in Web Viewer & HTML Steps to reproduce: 1. Create a chart. 2. Preveiw in Web Viewer/ HTML. Expected result: Chart can be previewed. Actual result: No chart is shown.
viewer/org.eclipse.birt.report.viewer/birt/WEB-INF/classes/org/eclipse/birt/report/service/ReportEngineService.java
Object parameterValue = parameters.get( parameterName );
			if ( parameterObj.isHidden( ) )
			{
				continue;
			}
			if ( parameterValue == null && !parameterObj.allowNull( ) )
			{
				missingParameter = true;
				break;
			}
			if ( IScalarParameterDefn.TYPE_STRING == parameterObj.getDataType( ) )
			{
				String parameterStringValue = (String) parameterValue;
				if ( parameterStringValue != null
						&& parameterStringValue.length( ) <= 0
						&& !parameterObj.allowBlank( ) )
				{
					missingParameter = true;
					break;
				}
			}
		}
		return missingParameter;
	}
	/**
	 * uses to clear the data cach.
	 * 
	 * @param dataSet
	 *            the dataset handle
	 * @throws BirtException