diff --git a/.travis.yml b/.travis.yml
index 4bbf5a0..1c5d7b2 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,5 +5,6 @@ script:
 
 jdk:
   - oraclejdk8
+  - openjdk7
 
 sudo: false
diff --git a/build.gradle b/build.gradle
index 9858f02..8135ae0 100644
--- a/build.gradle
+++ b/build.gradle
@@ -10,7 +10,7 @@ description = 'A Java client to communicate with a taskwarrior server (= taskd).
 group = 'de.aaschmid'
 version = '1.0-SNAPSHOT'
 
-sourceCompatibility = targetCompatibility = JavaVersion.VERSION_1_8
+sourceCompatibility = targetCompatibility = JavaVersion.VERSION_1_7
 
 repositories {
     mavenCentral()
diff --git a/src/main/java/de/aaschmid/taskwarrior/TaskwarriorClient.java b/src/main/java/de/aaschmid/taskwarrior/TaskwarriorClient.java
index ee9ed4b..44fdb90 100644
--- a/src/main/java/de/aaschmid/taskwarrior/TaskwarriorClient.java
+++ b/src/main/java/de/aaschmid/taskwarrior/TaskwarriorClient.java
@@ -11,11 +11,9 @@
 import java.security.KeyStore;
 import java.util.HashMap;
 import java.util.Map;
-import java.util.Set;
+import java.util.Map.Entry;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
-import java.util.stream.Collectors;
-import java.util.stream.Stream;
 
 import javax.net.ssl.SSLContext;
 
@@ -77,17 +75,16 @@ private TaskwarriorMessage receive(InputStream in) throws IOException {
     }
 
     private byte[] createByteArraysFor(TaskwarriorMessage message) {
-        // @formatter:off
-        String messageData = Stream.concat(
-                Stream.of(
-                        createHeadersFor(config.getAuthentication()),
-                        message.getHeaders()
-                    ).map(Map::entrySet).flatMap(Set::stream).map(e -> e.getKey() + SEPARATOR_HEADER_NAME_VALUE + e.getValue()),
-                Stream.of("", message.getPayload().orElse(""))
-            ).collect(Collectors.joining("\n"));
-        // @formatter:on
+        Map<String, String> headers = createHeadersFor(config.getAuthentication());
+        headers.putAll(message.getHeaders());
+
+        StringBuilder messageData = new StringBuilder();
+        for (Entry<String, String> e : headers.entrySet()) {
+            messageData.append(e.getKey() + SEPARATOR_HEADER_NAME_VALUE + e.getValue()).append("\n");
+        }
+        messageData.append("\n").append(message.getPayload());
 
-        byte[] bytes = messageData.getBytes(CHARSET_TRANSFER_MESSAGE);
+        byte[] bytes = messageData.toString().getBytes(CHARSET_TRANSFER_MESSAGE);
         return addFourByteBigEndianBinaryByteCountMessageLengthPrefix(bytes);
     }
 
@@ -128,7 +125,7 @@ private TaskwarriorMessage parseResponse(String message) {
 
         Map<String, String> headers = parseHeaders(header);
         if (payload.isEmpty() || "\n".equals(payload)) {
-            return new TaskwarriorMessage(headers);
+            payload = "";
         }
         return new TaskwarriorMessage(headers, payload);
     }
diff --git a/src/main/java/de/aaschmid/taskwarrior/internal/ManifestHelper.java b/src/main/java/de/aaschmid/taskwarrior/internal/ManifestHelper.java
index 2275c7b..3611062 100644
--- a/src/main/java/de/aaschmid/taskwarrior/internal/ManifestHelper.java
+++ b/src/main/java/de/aaschmid/taskwarrior/internal/ManifestHelper.java
@@ -2,41 +2,47 @@
 
 import java.io.IOException;
 import java.net.URL;
-import java.util.Optional;
 import java.util.jar.Manifest;
 
 public class ManifestHelper {
 
-    public static Optional<URL> getResourceUrlForClass(Class<?> clazz) {
+    public static URL getResourceUrlForClass(Class<?> clazz) {
         String className = clazz.getSimpleName() + ".class";
-        return Optional.ofNullable(clazz.getResource(className));
+        return clazz.getResource(className);
     }
 
-    public static Optional<String> getJarUrlForClass(Class<?> clazz) {
-        // @formatter:off
-        return getResourceUrlForClass(clazz)
-                .map(URL::toString)
-                .filter(p -> p.startsWith("jar:"))
-                .map(p -> p.substring(0, p.lastIndexOf("!") + 1));
-        // @formatter:on
+    public static String getJarUrlForClass(Class<?> clazz) {
+        URL resource = getResourceUrlForClass(clazz);
+        if (resource == null) {
+            return null;
+        }
+        String classPath = resource.toString();
+        if (classPath.startsWith("jar:")) {
+            return classPath.substring(0, classPath.lastIndexOf("!") + 1);
+        }
+        return null;
     }
 
-    public static Optional<String> getManifestAttributeValue(String jarUrl, String manifestAttributeKey) {
+    public static String getManifestAttributeValue(String jarUrl, String manifestAttributeKey) {
         try {
             Manifest manifest = new Manifest(new URL(jarUrl + "/META-INF/MANIFEST.MF").openStream());
-            return Optional.of(manifest.getMainAttributes().getValue(manifestAttributeKey));
+            return manifest.getMainAttributes().getValue(manifestAttributeKey);
 
         } catch (IOException e) {
-            return Optional.empty();
+            // TODO log this
+            return null;
         }
     }
 
     public static String getImplementationVersionFromManifest(String fallbackVersion) {
-        // @formatter:off
-        return Optional.of(ManifestHelper.class)
-                .flatMap(c -> getJarUrlForClass(c))
-                .flatMap(u -> getManifestAttributeValue(u, "Implementation-Version"))
-                .orElse(fallbackVersion);
-        // @formatter:on
+        String jarUrl = getJarUrlForClass(ManifestHelper.class);
+        if (jarUrl == null) {
+            return fallbackVersion;
+        }
+        String result = getManifestAttributeValue(jarUrl, "Implementation-Version");
+        if (result == null) {
+            return fallbackVersion;
+        }
+        return result;
     }
 }
diff --git a/src/main/java/de/aaschmid/taskwarrior/message/TaskwarriorMessage.java b/src/main/java/de/aaschmid/taskwarrior/message/TaskwarriorMessage.java
index efdc1e9..7749816 100644
--- a/src/main/java/de/aaschmid/taskwarrior/message/TaskwarriorMessage.java
+++ b/src/main/java/de/aaschmid/taskwarrior/message/TaskwarriorMessage.java
@@ -5,8 +5,6 @@
 
 import java.util.HashMap;
 import java.util.Map;
-import java.util.Objects;
-import java.util.Optional;
 
 public class TaskwarriorMessage {
 
@@ -15,26 +13,22 @@ public class TaskwarriorMessage {
     public static final String HEADER_CLIENT = "client";
 
     private final Map<String, String> headers;
-    private final Optional<String> payload;
-
-    public TaskwarriorMessage(Map<String, String> headers, Optional<String> payload) {
-        this.headers = new HashMap<>(Objects.requireNonNull(headers, "'headers' must not be null."));
-        this.payload = payload;
-    }
+    private final String payload;
 
     public TaskwarriorMessage(Map<String, String> headers, String payload) {
-        this(headers, Optional.of(requireNonNull(payload, "'payload' must not be null.")));
+        this.headers = new HashMap<>(requireNonNull(headers, "'headers' must not be null."));
+        this.payload = requireNonNull(payload, "'payload' must not be null");
     }
 
     public TaskwarriorMessage(Map<String, String> headers) {
-        this(headers, Optional.empty());
+        this(headers, "");
     }
 
     public Map<String, String> getHeaders() {
         return unmodifiableMap(headers);
     }
 
-    public Optional<String> getPayload() {
+    public String getPayload() {
         return payload;
     }
 
diff --git a/src/main/java/de/aaschmid/taskwarrior/ssl/KeyStoreBuilder.java b/src/main/java/de/aaschmid/taskwarrior/ssl/KeyStoreBuilder.java
index 88db37c..3a2058d 100644
--- a/src/main/java/de/aaschmid/taskwarrior/ssl/KeyStoreBuilder.java
+++ b/src/main/java/de/aaschmid/taskwarrior/ssl/KeyStoreBuilder.java
@@ -88,13 +88,13 @@ public KeyStore build() {
         }
 
         AtomicInteger idx = new AtomicInteger(0);
-        createCertificatesFor(caCertFile).forEach(c -> {
+        for (Certificate cert : createCertificatesFor(caCertFile)) {
             try {
-                result.setCertificateEntry("ca_" + idx.getAndIncrement(), c);
+                result.setCertificateEntry("ca_" + idx.getAndIncrement(), cert);
             } catch (KeyStoreException e) {
                 throw new TaskwarriorKeyStoreException(e, "Could not add CA certificate '%s' to keystore: %s", caCertFile, e.getMessage());
             }
-        });
+        }
 
         Certificate[] privateKeyCertsChain = createCertificatesFor(privateKeyCertFile).toArray(new Certificate[0]);
         PrivateKey privateKey = createPrivateKeyFor(privateKeyFile);