diff --git a/wrench-app/build.gradle b/wrench-app/build.gradle
index 423aa9c..9676dd8 100644
--- a/wrench-app/build.gradle
+++ b/wrench-app/build.gradle
@@ -62,8 +62,8 @@ android {
 dependencies {
     testImplementation 'junit:junit:4.12'
 
-    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2-alpha1'
-    androidTestImplementation 'com.android.support.test:runner:1.0.2-alpha1'
+    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2-beta1'
+    androidTestImplementation 'com.android.support.test:runner:1.0.2-beta1'
     androidTestImplementation 'android.arch.persistence.room:testing:1.1.0-beta2'
 
     annotationProcessor "android.arch.lifecycle:compiler:1.1.1"
diff --git a/wrench-app/src/androidTest/java/com/izettle/wrench/provider/WrenchProviderTest.java b/wrench-app/src/androidTest/java/com/izettle/wrench/provider/WrenchProviderTest.java
index dbd2f4e..fa19a59 100644
--- a/wrench-app/src/androidTest/java/com/izettle/wrench/provider/WrenchProviderTest.java
+++ b/wrench-app/src/androidTest/java/com/izettle/wrench/provider/WrenchProviderTest.java
@@ -171,6 +171,6 @@ private Nut getNut(String value) {
     }
 
     private Bolt getBolt(String key) {
-        return new Bolt(0, "bolttype", key, "boltvalue");
+        return new Bolt(0L, "bolttype", key, "boltvalue");
     }
 }
\ No newline at end of file
diff --git a/wrench-core/build.gradle b/wrench-core/build.gradle
index a6f4929..a4d5d83 100644
--- a/wrench-core/build.gradle
+++ b/wrench-core/build.gradle
@@ -1,14 +1,11 @@
 apply plugin: 'com.android.library'
-apply plugin: 'kotlin-android'
 
 android {
     compileSdkVersion 27
 
     defaultConfig {
-        minSdkVersion 15
+        minSdkVersion 1
         targetSdkVersion 27
-        versionCode 1
-        versionName "1.0"
 
         testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
 
@@ -43,7 +40,6 @@ android {
 dependencies {
     testImplementation 'junit:junit:4.12'
     implementation 'com.android.support:support-annotations:27.1.1'
-    implementation "org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version"
 }
 
 apply from: rootProject.file('gradle/gradle-mvn-push.gradle')
diff --git a/wrench-core/src/main/java/com/izettle/wrench/core/Bolt.java b/wrench-core/src/main/java/com/izettle/wrench/core/Bolt.java
new file mode 100644
index 0000000..5702eff
--- /dev/null
+++ b/wrench-core/src/main/java/com/izettle/wrench/core/Bolt.java
@@ -0,0 +1,123 @@
+package com.izettle.wrench.core;
+
+import android.content.ContentValues;
+import android.database.Cursor;
+import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
+import android.support.annotation.StringDef;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+public class Bolt {
+    @NonNull
+    @BoltType
+    private final String type;
+    @NonNull
+    private final String key;
+    @Nullable
+    private final String value;
+    private long id;
+
+    public Bolt(Long id, @NonNull String type, @NonNull String key, @Nullable String value) {
+        this.id = id;
+        this.type = type;
+        this.key = key;
+        this.value = value;
+    }
+
+    public Bolt() {
+        type = "";
+        key = "";
+        value = null;
+    }
+
+    public static Bolt fromContentValues(ContentValues values) {
+        Long id = values.getAsLong(ColumnNames.Bolt.COL_ID);
+        @BoltType
+        String type = values.getAsString(ColumnNames.Bolt.COL_TYPE);
+        String key = values.getAsString(ColumnNames.Bolt.COL_KEY);
+        String value = values.getAsString(ColumnNames.Bolt.COL_VALUE);
+
+        return new Bolt(id, type, key, value);
+    }
+
+    public static Bolt fromCursor(Cursor cursor) {
+        long id = getNullsafeLong(cursor, ColumnNames.Bolt.COL_ID);
+        @BoltType
+        String type = getNullsafeString(cursor, ColumnNames.Bolt.COL_TYPE);
+        String key = getNullsafeString(cursor, ColumnNames.Bolt.COL_KEY);
+        String value = cursor.getString(cursor.getColumnIndexOrThrow(ColumnNames.Bolt.COL_VALUE));
+
+        return new Bolt(id, type, key, value);
+    }
+
+    @NonNull
+    private static Long getNullsafeLong(Cursor cursor, String columnName) {
+        int columnIndex = cursor.getColumnIndexOrThrow(columnName);
+        if (cursor.isNull(columnIndex)) {
+            throw new IllegalStateException(columnName + " was null");
+        }
+        return cursor.getLong(columnIndex);
+    }
+
+    @NonNull
+    private static String getNullsafeString(Cursor cursor, String columnName) {
+        int columnIndex = cursor.getColumnIndexOrThrow(columnName);
+        if (cursor.isNull(columnIndex)) {
+            throw new IllegalStateException(columnName + " was null");
+        }
+        return cursor.getString(columnIndex);
+    }
+
+    @NonNull
+    public String getKey() {
+        return key;
+    }
+
+    @NonNull
+    public String getType() {
+        return type;
+    }
+
+    @Nullable
+    public String getValue() {
+        return value;
+    }
+
+    public ContentValues toContentValues() {
+        ContentValues contentValues = new ContentValues();
+
+        contentValues.put(ColumnNames.Bolt.COL_ID, id);
+        contentValues.put(ColumnNames.Bolt.COL_KEY, key);
+        contentValues.put(ColumnNames.Bolt.COL_VALUE, value);
+        contentValues.put(ColumnNames.Bolt.COL_TYPE, type);
+
+        return contentValues;
+    }
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(long id) {
+        this.id = id;
+    }
+
+    @NonNull
+    public Bolt copy(Long id, String type, String key, String value) {
+        return new Bolt(id, type, key, value);
+    }
+
+    @Retention(RetentionPolicy.SOURCE)
+    @StringDef({TYPE.BOOLEAN, TYPE.STRING, TYPE.INTEGER, TYPE.ENUM})
+    public @interface BoltType {
+    }
+
+    public interface TYPE {
+        String BOOLEAN = "boolean";
+        String STRING = "string";
+        String INTEGER = "integer";
+        String ENUM = "enum";
+    }
+}
diff --git a/wrench-core/src/main/java/com/izettle/wrench/core/Bolt.kt b/wrench-core/src/main/java/com/izettle/wrench/core/Bolt.kt
deleted file mode 100644
index d6d6579..0000000
--- a/wrench-core/src/main/java/com/izettle/wrench/core/Bolt.kt
+++ /dev/null
@@ -1,70 +0,0 @@
-package com.izettle.wrench.core
-
-import android.content.ContentValues
-import android.database.Cursor
-import android.support.annotation.StringDef
-
-data class Bolt(var id: Long = 0,
-                @BoltType val type: String,
-                val key: String = "",
-                val value: String? = null) {
-
-    fun toContentValues(): ContentValues {
-        val contentValues = ContentValues()
-
-        contentValues.put(ColumnNames.Bolt.COL_ID, id)
-        contentValues.put(ColumnNames.Bolt.COL_KEY, key)
-        contentValues.put(ColumnNames.Bolt.COL_VALUE, value)
-        contentValues.put(ColumnNames.Bolt.COL_TYPE, type)
-
-        return contentValues
-    }
-
-    @StringDef(TYPE.BOOLEAN, TYPE.STRING, TYPE.INTEGER, TYPE.ENUM)
-    @Retention(AnnotationRetention.SOURCE)
-    annotation class BoltType
-
-    object TYPE {
-        const val BOOLEAN = "boolean"
-        const val STRING = "string"
-        const val INTEGER = "integer"
-        const val ENUM = "enum"
-    }
-
-    companion object {
-
-        @JvmStatic
-        fun fromContentValues(values: ContentValues): Bolt {
-
-            return Bolt(id = values.getAsLong(ColumnNames.Bolt.COL_ID) ?: 0,
-                    type = values.getAsString(ColumnNames.Bolt.COL_TYPE),
-                    key = values.getAsString(ColumnNames.Bolt.COL_KEY),
-                    value = values.getAsString(ColumnNames.Bolt.COL_VALUE))
-        }
-
-        @JvmStatic
-        fun fromCursor(cursor: Cursor): Bolt {
-            return Bolt(id = cursor.getLongOrThrow(ColumnNames.Bolt.COL_ID),
-                    type = cursor.getStringOrThrow(ColumnNames.Bolt.COL_TYPE),
-                    key = cursor.getStringOrThrow(ColumnNames.Bolt.COL_KEY),
-                    value = cursor.getStringOrNull(ColumnNames.Bolt.COL_VALUE)
-            )
-        }
-    }
-}
-
-
-private fun Cursor.getStringOrThrow(columnName: String): String = getStringOrNull(columnName)!!
-
-private fun Cursor.getStringOrNull(columnName: String): String? {
-    val index = getColumnIndexOrThrow(columnName)
-    return if (isNull(index)) null else getString(index)
-}
-
-private fun Cursor.getLongOrThrow(columnName: String): Long = getLongOrNull(columnName)!!
-
-private fun Cursor.getLongOrNull(columnName: String): Long? {
-    val index = getColumnIndexOrThrow(columnName)
-    return if (isNull(index)) null else getLong(index)
-}
-
diff --git a/wrench-core/src/main/java/com/izettle/wrench/core/ColumnNames.java b/wrench-core/src/main/java/com/izettle/wrench/core/ColumnNames.java
new file mode 100644
index 0000000..5e4fe72
--- /dev/null
+++ b/wrench-core/src/main/java/com/izettle/wrench/core/ColumnNames.java
@@ -0,0 +1,16 @@
+package com.izettle.wrench.core;
+
+public final class ColumnNames {
+    public interface Bolt {
+        String COL_KEY = "configurationKey";
+        String COL_ID = "id";
+        String COL_VALUE = "value";
+        String COL_TYPE = "configurationType";
+    }
+
+    public interface Nut {
+        String COL_ID = "id";
+        String COL_VALUE = "value";
+        String COL_CONFIG_ID = "configurationId";
+    }
+}
diff --git a/wrench-core/src/main/java/com/izettle/wrench/core/ColumnNames.kt b/wrench-core/src/main/java/com/izettle/wrench/core/ColumnNames.kt
deleted file mode 100644
index 85af12e..0000000
--- a/wrench-core/src/main/java/com/izettle/wrench/core/ColumnNames.kt
+++ /dev/null
@@ -1,16 +0,0 @@
-package com.izettle.wrench.core
-
-class ColumnNames {
-    object Bolt {
-        const val COL_KEY = "configurationKey"
-        const val COL_ID = "id"
-        const val COL_VALUE = "value"
-        const val COL_TYPE = "configurationType"
-    }
-
-    object Nut {
-        const val COL_ID = "id"
-        const val COL_VALUE = "value"
-        const val COL_CONFIG_ID = "configurationId"
-    }
-}
diff --git a/wrench-core/src/main/java/com/izettle/wrench/core/Nut.java b/wrench-core/src/main/java/com/izettle/wrench/core/Nut.java
new file mode 100644
index 0000000..e1bde4b
--- /dev/null
+++ b/wrench-core/src/main/java/com/izettle/wrench/core/Nut.java
@@ -0,0 +1,33 @@
+package com.izettle.wrench.core;
+
+import android.content.ContentValues;
+
+public class Nut {
+    private final long id;
+    private final long configurationId;
+    private final String value;
+
+    public Nut(long configurationId, String value) {
+        this.id = 0;
+        this.configurationId = configurationId;
+        this.value = value;
+    }
+
+    public Nut(long id, long configurationId, String value) {
+        this.id = id;
+        this.configurationId = configurationId;
+        this.value = value;
+    }
+
+    public ContentValues toContentValues() {
+        ContentValues contentValues = new ContentValues();
+        if (id > 0) {
+            contentValues.put(ColumnNames.Nut.COL_ID, id);
+        }
+
+        contentValues.put(ColumnNames.Nut.COL_CONFIG_ID, configurationId);
+        contentValues.put(ColumnNames.Nut.COL_VALUE, value);
+
+        return contentValues;
+    }
+}
diff --git a/wrench-core/src/main/java/com/izettle/wrench/core/Nut.kt b/wrench-core/src/main/java/com/izettle/wrench/core/Nut.kt
deleted file mode 100644
index 34e107a..0000000
--- a/wrench-core/src/main/java/com/izettle/wrench/core/Nut.kt
+++ /dev/null
@@ -1,21 +0,0 @@
-package com.izettle.wrench.core
-
-import android.content.ContentValues
-
-data class Nut(val id: Long = 0,
-               val configurationId: Long = 0,
-               val value: String? = null) {
-
-    constructor(configurationId: Long, value: String?) : this(0, configurationId, value)
-
-    fun toContentValues(): ContentValues {
-        val contentValues = ContentValues()
-        if (id > 0) {
-            contentValues.put(ColumnNames.Nut.COL_ID, id)
-        }
-        contentValues.put(ColumnNames.Nut.COL_CONFIG_ID, configurationId)
-        contentValues.put(ColumnNames.Nut.COL_VALUE, value)
-
-        return contentValues
-    }
-}
diff --git a/wrench-core/src/main/java/com/izettle/wrench/core/WrenchProviderContract.java b/wrench-core/src/main/java/com/izettle/wrench/core/WrenchProviderContract.java
new file mode 100644
index 0000000..4bec9b4
--- /dev/null
+++ b/wrench-core/src/main/java/com/izettle/wrench/core/WrenchProviderContract.java
@@ -0,0 +1,42 @@
+package com.izettle.wrench.core;
+
+import android.net.Uri;
+
+public final class WrenchProviderContract {
+    public static final String WRENCH_AUTHORITY = BuildConfig.WRENCH_AUTHORITY;
+
+    public static final String WRENCH_API_VERSION = "API_VERSION";
+
+    private static Uri boltUri = Uri.parse("content://" + WRENCH_AUTHORITY + "/currentConfiguration");
+    private static Uri nutUri = Uri.parse("content://" + WRENCH_AUTHORITY + "/predefinedConfigurationValue");
+
+    public static Uri boltUri(long id) {
+        return boltUri
+                .buildUpon()
+                .appendPath(String.valueOf(id))
+                .appendQueryParameter(WRENCH_API_VERSION, String.valueOf(BuildConfig.WRENCH_API_VERSION))
+                .build();
+    }
+
+    public static Uri boltUri(String key) {
+        return boltUri
+                .buildUpon()
+                .appendPath(key)
+                .appendQueryParameter(WRENCH_API_VERSION, String.valueOf(BuildConfig.WRENCH_API_VERSION))
+                .build();
+    }
+
+    public static Uri boltUri() {
+        return boltUri
+                .buildUpon()
+                .appendQueryParameter(WRENCH_API_VERSION, String.valueOf(BuildConfig.WRENCH_API_VERSION))
+                .build();
+    }
+
+    public static Uri nutUri() {
+        return nutUri
+                .buildUpon()
+                .appendQueryParameter(WRENCH_API_VERSION, String.valueOf(BuildConfig.WRENCH_API_VERSION))
+                .build();
+    }
+}
diff --git a/wrench-core/src/main/java/com/izettle/wrench/core/WrenchProviderContract.kt b/wrench-core/src/main/java/com/izettle/wrench/core/WrenchProviderContract.kt
deleted file mode 100644
index b54c702..0000000
--- a/wrench-core/src/main/java/com/izettle/wrench/core/WrenchProviderContract.kt
+++ /dev/null
@@ -1,47 +0,0 @@
-package com.izettle.wrench.core
-
-import android.net.Uri
-
-object WrenchProviderContract {
-    const val WRENCH_AUTHORITY = BuildConfig.WRENCH_AUTHORITY
-
-    const val WRENCH_API_VERSION = "API_VERSION"
-
-    private val boltUri = Uri.parse("content://$WRENCH_AUTHORITY/currentConfiguration")
-    private val nutUri = Uri.parse("content://$WRENCH_AUTHORITY/predefinedConfigurationValue")
-
-    @JvmStatic
-    fun boltUri(id: Long): Uri {
-        return boltUri
-                .buildUpon()
-                .appendPath(id.toString())
-                .appendQueryParameter(WRENCH_API_VERSION, BuildConfig.WRENCH_API_VERSION.toString())
-                .build()
-
-    }
-
-    @JvmStatic
-    fun boltUri(key: String): Uri {
-        return boltUri
-                .buildUpon()
-                .appendPath(key)
-                .appendQueryParameter(WRENCH_API_VERSION, BuildConfig.WRENCH_API_VERSION.toString())
-                .build()
-    }
-
-    @JvmStatic
-    fun boltUri(): Uri {
-        return boltUri
-                .buildUpon()
-                .appendQueryParameter(WRENCH_API_VERSION, BuildConfig.WRENCH_API_VERSION.toString())
-                .build()
-    }
-
-    @JvmStatic
-    fun nutUri(): Uri {
-        return nutUri
-                .buildUpon()
-                .appendQueryParameter(WRENCH_API_VERSION, BuildConfig.WRENCH_API_VERSION.toString())
-                .build()
-    }
-}
diff --git a/wrench-prefs/src/main/java/com/izettle/wrench/preferences/WrenchPreferences.kt b/wrench-prefs/src/main/java/com/izettle/wrench/preferences/WrenchPreferences.kt
index afbe519..3d10ed5 100644
--- a/wrench-prefs/src/main/java/com/izettle/wrench/preferences/WrenchPreferences.kt
+++ b/wrench-prefs/src/main/java/com/izettle/wrench/preferences/WrenchPreferences.kt
@@ -26,7 +26,7 @@ open class WrenchPreferences(context: Context) {
             }
         }
 
-        return Bolt(type = boltType, key = key)
+        return Bolt(0, boltType, key, null)
     }
 
     private fun insertBolt(contentResolver: ContentResolver, bolt: Bolt): Uri? {
@@ -37,7 +37,7 @@ open class WrenchPreferences(context: Context) {
         var bolt = getBolt(contentResolver, Bolt.TYPE.ENUM, key) ?: return defValue
 
         if (bolt.id == 0L) {
-            bolt = bolt.copy(key = key, type = Bolt.TYPE.ENUM, value = defValue.toString())
+            bolt = bolt.copy(bolt.id, key, Bolt.TYPE.ENUM, defValue.toString())
             val uri = insertBolt(contentResolver, bolt)
             bolt.id = uri!!.lastPathSegment.toLong()
 
@@ -54,7 +54,7 @@ open class WrenchPreferences(context: Context) {
         var bolt = getBolt(contentResolver, Bolt.TYPE.STRING, key) ?: return defValue
 
         if (bolt.id == 0L) {
-            bolt = bolt.copy(key = key, type = Bolt.TYPE.STRING, value = defValue)
+            bolt = bolt.copy(bolt.id, key, Bolt.TYPE.STRING, defValue)
             insertBolt(contentResolver, bolt)
         }
 
@@ -65,7 +65,7 @@ open class WrenchPreferences(context: Context) {
         var bolt = getBolt(contentResolver, Bolt.TYPE.BOOLEAN, key) ?: return defValue
 
         if (bolt.id == 0L) {
-            bolt = bolt.copy(key = key, type = Bolt.TYPE.BOOLEAN, value = defValue.toString())
+            bolt = bolt.copy(bolt.id, key, Bolt.TYPE.BOOLEAN, defValue.toString())
             insertBolt(contentResolver, bolt)
         }
 
@@ -76,7 +76,7 @@ open class WrenchPreferences(context: Context) {
         var bolt = getBolt(contentResolver, Bolt.TYPE.INTEGER, key) ?: return defValue
 
         if (bolt.id == 0L) {
-            bolt = bolt.copy(key = key, type = Bolt.TYPE.INTEGER, value = defValue.toString())
+            bolt = bolt.copy(bolt.id, key, Bolt.TYPE.INTEGER, defValue.toString())
             insertBolt(contentResolver, bolt)
         }
 
diff --git a/wrench-sample/build.gradle b/wrench-sample/build.gradle
index e5e39be..36fb4d3 100644
--- a/wrench-sample/build.gradle
+++ b/wrench-sample/build.gradle
@@ -50,8 +50,9 @@ dependencies {
     testImplementation 'junit:junit:4.12'
     testImplementation 'org.mockito:mockito-core:2.18.0'
 
-    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2-alpha1'
-    androidTestImplementation 'com.android.support.test:runner:1.0.2-alpha1'
+    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2-beta1'
+    androidTestImplementation 'com.android.support.test:runner:1.0.2-beta1'
+    androidTestImplementation 'com.android.support.test:rules:1.0.2-beta1'
     androidTestImplementation project(":wrench-core")
     androidTestImplementation project(":wrench-prefs")
 
diff --git a/wrench-sample/src/androidTest/java/com/example/wrench/LaunchTest.java b/wrench-sample/src/androidTest/java/com/example/wrench/LaunchTest.java
index cbcb93e..746896e 100644
--- a/wrench-sample/src/androidTest/java/com/example/wrench/LaunchTest.java
+++ b/wrench-sample/src/androidTest/java/com/example/wrench/LaunchTest.java
@@ -108,7 +108,7 @@ private static Bolt getBolt(ContentResolver contentResolver, @Bolt.BoltType Stri
                 cursor.close();
             }
         }
-        return new Bolt(0, type, key, "");
+        return new Bolt(0L, type, key, "");
     }
 
     private static Uri insertBolt(ContentResolver contentResolver, Bolt bolt) {
diff --git a/wrench-sample/src/main/java/com/example/wrench/BoltLiveData/WrenchLiveData.java b/wrench-sample/src/main/java/com/example/wrench/BoltLiveData/WrenchLiveData.java
index f7fddf5..dfedfd2 100644
--- a/wrench-sample/src/main/java/com/example/wrench/BoltLiveData/WrenchLiveData.java
+++ b/wrench-sample/src/main/java/com/example/wrench/BoltLiveData/WrenchLiveData.java
@@ -65,7 +65,7 @@ private static Bolt getBolt(ContentResolver contentResolver, @Bolt.BoltType Stri
                 cursor.close();
             }
         }
-        return new Bolt(0, type, key, "");
+        return new Bolt(0L, type, key, "");
     }
 
     String getType() {
diff --git a/wrench-service/src/main/java/com/izettle/wrench/service/WrenchService.kt b/wrench-service/src/main/java/com/izettle/wrench/service/WrenchService.kt
index 0c855d2..19f5a3e 100644
--- a/wrench-service/src/main/java/com/izettle/wrench/service/WrenchService.kt
+++ b/wrench-service/src/main/java/com/izettle/wrench/service/WrenchService.kt
@@ -82,6 +82,6 @@ class WrenchService : IntentService("WrenchService") {
             }
         }
 
-        return Bolt(type = boltType, key = key)
+        return Bolt(0, boltType, key, null)
     }
 }