Bug 202236 When select NULL value for multi-value parameter, cause NPE.
Description: When select NULL value for multi-value parameter, cause NPE. Build number: 2.2.1 Steps to reproduce: 1, New a list parameter, check Allow multi-value, uncheck isRequired 2, Select parameter data type as Date 3, Add some items into list 4, Preview 5, Select Null Value item in list Expected result: Can accept Null value for multi-value parameter Actual result: Cause NPE.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/impl/EngineTask.java
{
					String paramName = param.getName( );
					Object paramValue = runValues.get( paramName );
					buffer.append( paramName );
					buffer.append( ":" );
					buffer.append( paramValue );
					buffer.append( "\n" );
					return true;
				}
				boolean visitParameterGroup( ParameterGroupHandle group,
						Object value )
				{
					return visitParametersInGroup( group, value );
				}
			}.visit( (ReportDesignHandle) runnable.getDesignHandle( ), null );
			log.log( Level.FINE, "Running the report with paramters: {0}",
					buffer );
		}
	}
	/**
	 * validate whether the parameter value is a valid value for the parameter
	 * 
	 * @param p
	 *            the parameter to be verified
	 * @param paramValue
	 *            the value for the parameter
	 * @return true if the given parameter value is valid; false otherwise
	 */
	private boolean validateScalarParameter( ScalarParameterHandle paramHandle )
			throws ParameterValidationException