@Test(expected=NullPointerException.class)
public void addHeaderMethodShouldThrowNpeWhenKeyIsNull() {

	// Given
	String nullKey = null;
	String value = "test";
	
	String url = "test";
	HttpMethod method = HttpMethod.GET;
	VolleyerConfiguration configuration = DefaultVolleyerConfigurationFactory.create();
	TestPurposeRequestBuilder builder = new TestPurposeRequestBuilder(requestQueue, configuration, url, method);
	
	// When & Then
	builder.addHeader(nullKey, value);
}