Fixes builder regression: pop() used to be nullable

.travis.yml

@@ -2,8 +2,8 @@ language: android
 
 android:
   components:
-    - build-tools-21.1.2
-    - android-21
+    - build-tools-22.0.1
+    - android-22
   licenses:
     - android-sdk-license-5be876d5
 

CHANGELOG.md

@@ -1,6 +1,10 @@
 Change Log
 ==========
 
+Version 0.12 *(2015-08-13)*
+------
+* Fix: History.Builder#pop is nullable again, and adds History.Builder#isEmpty.
+
 Version 0.11 *(2015-08-11)*
 ------
 * Fix: No longer persists an empty list of states if the filter excludes everything.

flow/build.gradle

@@ -18,6 +18,7 @@ android {
 }
 
 dependencies {
+  compile 'com.android.support:support-annotations:22.2.1'
   testCompile 'junit:junit:4.10'
   testCompile 'org.easytesting:fest-assert-core:2.0M10'
 }

flow/src/main/java/flow/History.java

@@ -18,6 +18,7 @@
 
 import android.os.Bundle;
 import android.os.Parcelable;
+import android.support.annotation.Nullable;
 import android.util.SparseArray;
 import android.view.View;
 import java.util.ArrayDeque;
@@ -217,11 +218,20 @@ public Builder addAll(Collection<Object> c) {
       return this;
     }
 
-    public Object peek() {
-      return history.peek().state;
+    @Nullable public Object peek() {
+      final Entry peek = history.peek();
+      return peek == null ? null : peek.state;
     }
 
+    public boolean isEmpty() {
+      return peek() == null;
+    }
+
+    /** @throws IllegalStateException if empty */
     public Object pop() {
+      if (isEmpty()) {
+        throw new IllegalStateException("Cannot pop from an empty builder");
+      }
       Entry entry = history.pop();
       entryMemory.put(entry.state, entry);
       return entry.state;

flow/src/test/java/flow/FlowTest.java

@@ -24,6 +24,7 @@
 import static flow.Flow.TraversalCallback;
 import static java.util.Arrays.asList;
 import static org.fest.assertions.api.Assertions.assertThat;
+import static org.fest.assertions.api.Fail.fail;
 
 public class FlowTest {
   static class Uno {
@@ -287,4 +288,26 @@ public int hashCode() {
 
     assertThat(flow.goBack()).isFalse();
   }
+
+  @Test public void emptyBuilderPeekIsNullable() {
+    assertThat(History.emptyBuilder().peek()).isNull();
+  }
+
+  @Test public void emptyBuilderPopThrows() {
+    try {
+      History.emptyBuilder().pop();
+      fail("Should throw");
+    } catch (IllegalStateException e) {
+      // pass
+    }
+  }
+
+  @Test public void isEmpty() {
+    final History.Builder builder = History.emptyBuilder();
+    assertThat(builder.isEmpty()).isTrue();
+    builder.push("foo");
+    assertThat(builder.isEmpty()).isFalse();
+    builder.pop();
+    assertThat(builder.isEmpty()).isTrue();
+  }
 }