fix NPE in PrometheusMvcEndpoint.value() (#256)

Author: sunghyuk

simpleclient_spring_boot/src/main/java/io/prometheus/client/spring/boot/PrometheusMvcEndpoint.java

@@ -28,7 +28,7 @@ public PrometheusMvcEndpoint(PrometheusEndpoint delegate) {
   )
   @ResponseBody
   public ResponseEntity value(
-          @RequestParam(value = "name[]", required = false) Set<String> name) {
+          @RequestParam(value = "name[]", required = false, defaultValue = "") Set<String> name) {
     if (!getDelegate().isEnabled()) {
       // Shouldn't happen - MVC endpoint shouldn't be registered when delegate's
       // disabled

simpleclient_spring_boot/src/test/java/io/prometheus/client/spring/boot/PrometheusMvcEndpointTest.java

@@ -0,0 +1,57 @@
+package io.prometheus.client.spring.boot;
+
+import io.prometheus.client.exporter.common.TextFormat;
+import org.apache.commons.lang3.StringUtils;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.boot.test.SpringApplicationConfiguration;
+import org.springframework.boot.test.TestRestTemplate;
+import org.springframework.boot.test.WebIntegrationTest;
+import org.springframework.http.HttpEntity;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+import org.springframework.web.client.RestTemplate;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@SpringApplicationConfiguration(DummyBootApplication.class)
+@WebIntegrationTest(randomPort = true)
+public class PrometheusMvcEndpointTest {
+
+    @Value("${local.server.port}")
+    int localServerPort;
+
+    RestTemplate template = new TestRestTemplate();
+
+    @Test
+    public void testNameParamIsNull() throws Exception {
+        ResponseEntity metricsResponse = template.exchange(getBaseUrl() + "/prometheus", HttpMethod.GET, getEntity(), String.class);
+
+        assertEquals(HttpStatus.OK, metricsResponse.getStatusCode());
+        assertTrue(StringUtils.deleteWhitespace(TextFormat.CONTENT_TYPE_004).equals(metricsResponse.getHeaders().getContentType().toString()));
+    }
+
+    @Test
+    public void testNameParamIsNotNull() {
+        ResponseEntity metricsResponse = template.exchange(getBaseUrl() + "/prometheus?name[]=foo_bar", HttpMethod.GET, getEntity(), String.class);
+
+        assertEquals(HttpStatus.OK, metricsResponse.getStatusCode());
+        assertTrue(StringUtils.deleteWhitespace(TextFormat.CONTENT_TYPE_004).equals(metricsResponse.getHeaders().getContentType().toString()));
+    }
+
+    public HttpEntity getEntity() {
+        HttpHeaders headers = new HttpHeaders();
+        headers.set("Accept", "text/plain; version=0.0.4; charset=utf-8");
+        return new HttpEntity(headers);
+    }
+
+    private String getBaseUrl() {
+        return "http://localhost:" + localServerPort;
+    }
+}