fix npe (fixes #522, via #525)

allure-plugin-api/src/main/java/io/qameta/allure/entity/TestResult.java

@@ -96,8 +96,8 @@ public Optional<String> findOneLabel(final LabelName name) {
     public Optional<String> findOneLabel(final String name) {
         return getLabels().stream()
                 .filter(label -> name.equals(label.getName()))
-                .map(Label::getValue)
-                .findAny();
+                .findAny()
+                .map(Label::getValue);
     }
 
     public void addLabelIfNotExists(final LabelName name, final String value) {

allure-plugin-api/src/test/java/io/qameta/allure/entity/LabelsTest.java

@@ -0,0 +1,41 @@
+package io.qameta.allure.entity;
+
+import org.junit.Test;
+
+import java.util.List;
+import java.util.Optional;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * @author charlie (Dmitry Baev).
+ */
+public class LabelsTest {
+
+    @Test
+    public void shouldFindLabelsInEmptyArray() throws Exception {
+        final Optional<String> found = new TestResult().findOneLabel("hey");
+        assertThat(found)
+                .isEmpty();
+    }
+
+    @Test
+    public void shouldFindOneWithNullValue() throws Exception {
+        final TestResult result = new TestResult();
+        result.getLabels().add(new Label().setName("hey").setValue(null));
+        final Optional<String> found = result.findOneLabel("hey");
+        assertThat(found)
+                .isEmpty();
+    }
+
+    @Test
+    public void shouldFindAllWithNullValue() throws Exception {
+        final TestResult result = new TestResult();
+        result.getLabels().add(new Label().setName("hey").setValue(null));
+        result.getLabels().add(new Label().setName("hey").setValue("a"));
+        result.getLabels().add(new Label().setName("hey").setValue("b"));
+        final List<String> found = result.findAllLabels("hey");
+        assertThat(found)
+                .containsExactlyInAnyOrder(null, "a", "b");
+    }
+}