jmeter Beanshell PostProcessor remove header throws exception

When I was using BeanShell PostProcessor to delete the header，there is a problem my code:

import org.apache.jmeter.protocol.http.control.Header; 

sampler.getHeaderManager().removeHeaderNamed("Authorization");

exception:

2017/05/18 15:24:52 ERROR - jmeter.util.BeanShellInterpreter: Error invoking bsh method: eval   Sourced file: inline evaluation of: ``import org.apache.jmeter.protocol.http.control.Header;   sampler.getHeaderManage . . . '' : Attempt to resolve method: getHeaderManager() on undefined variable or class name: sampler 

2017/05/18 15:24:52 WARN  - jmeter.extractor.BeanShellPostProcessor: Problem in BeanShell script org.apache.jorphan.util.JMeterException: Error invoking bsh method: eval   Sourced file: inline evaluation of: ``import org.apache.jmeter.protocol.http.control.Header;   sampler.getHeaderManage . . . '' : Attempt to resolve method: getHeaderManager() on undefined variable or class name: sampler 

somebody help me