fix: convert result from secret manager property resolver from ByteSt…

spring-cloud-gcp-secretmanager/src/main/java/com/google/cloud/spring/secretmanager/SecretManagerPropertySource.java

@@ -18,6 +18,7 @@
 
 import com.google.cloud.secretmanager.v1.SecretVersionName;
 import com.google.cloud.spring.core.GcpProjectIdProvider;
+import com.google.protobuf.ByteString;
 import org.springframework.core.env.EnumerablePropertySource;
 
 /**
@@ -44,7 +45,8 @@ public Object getProperty(String name) {
         SecretManagerPropertyUtils.getSecretVersionName(name, this.projectIdProvider);
 
     if (secretIdentifier != null) {
-      return getSource().getSecretByteString(secretIdentifier);
+      ByteString secretByteString = getSource().getSecretByteString(secretIdentifier);
+      return secretByteString == null ? null : secretByteString.toStringUtf8();
     } else {
       return null;
     }

spring-cloud-gcp-secretmanager/src/test/java/com/google/cloud/spring/secretmanager/SecretManagerPropertySourceTests.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2017-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.cloud.spring.secretmanager;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import com.google.cloud.secretmanager.v1.SecretVersionName;
+import com.google.cloud.spring.core.GcpProjectIdProvider;
+import com.google.protobuf.ByteString;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mockito;
+
+public class SecretManagerPropertySourceTests {
+  private static final GcpProjectIdProvider DEFAULT_PROJECT_ID_PROVIDER = () -> "defaultProject";
+
+  private SecretManagerTemplate secretManagerTemplate;
+
+  private SecretManagerPropertySource source;
+
+  @BeforeEach
+  void setupMocks() {
+    this.secretManagerTemplate = mock(SecretManagerTemplate.class);
+    source = new SecretManagerPropertySource("name", secretManagerTemplate, DEFAULT_PROJECT_ID_PROVIDER);
+  }
+
+  @Test
+  void testSecret() {
+    String expected = "secret";
+    when(this.secretManagerTemplate.getSecretByteString(Mockito.any(SecretVersionName.class))).thenReturn(ByteString.copyFromUtf8(expected));
+    assertEquals(expected, source.getProperty("sm://property-name"));
+  }
+
+  @Test
+  void testMissingSecret() {
+    when(this.secretManagerTemplate.getSecretByteString(Mockito.any(SecretVersionName.class))).thenReturn(null);
+    assertNull(source.getProperty("sm://property-name"));
+  }
+}