diff --git a/value/src/main/java/com/google/auto/value/processor/BuilderSpec.java b/value/src/main/java/com/google/auto/value/processor/BuilderSpec.java
index 46f17cf05b..9b372af014 100644
--- a/value/src/main/java/com/google/auto/value/processor/BuilderSpec.java
+++ b/value/src/main/java/com/google/auto/value/processor/BuilderSpec.java
@@ -163,13 +163,19 @@ ImmutableSet<ExecutableElement> toBuilderMethods(
       return builderMethods;
     }
 
+    /**
+     * Returns the types that are referenced by abstract methods in the builder, either as
+     * parameters or as return types.
+     */
     Set<TypeMirror> referencedTypes() {
       Set<TypeMirror> types = new TypeMirrorSet();
       for (ExecutableElement method :
           ElementFilter.methodsIn(builderTypeElement.getEnclosedElements())) {
-        types.add(method.getReturnType());
-        for (VariableElement parameter : method.getParameters()) {
-          types.add(parameter.asType());
+        if (method.getModifiers().contains(Modifier.ABSTRACT)) {
+          types.add(method.getReturnType());
+          for (VariableElement parameter : method.getParameters()) {
+            types.add(parameter.asType());
+          }
         }
       }
       return types;
diff --git a/value/src/main/java/com/google/auto/value/processor/autovalue.vm b/value/src/main/java/com/google/auto/value/processor/autovalue.vm
index 3a679fc33c..7b9ea92fd0 100644
--- a/value/src/main/java/com/google/auto/value/processor/autovalue.vm
+++ b/value/src/main/java/com/google/auto/value/processor/autovalue.vm
@@ -40,7 +40,11 @@ ${gwtCompatibleAnnotation}
       ${p.nullableAnnotation}$p.type $p #if ($foreach.hasNext) , #end
 #end ) {
 #foreach ($p in $props)
-  #if (!$p.kind.primitive && !$p.nullable && $builderTypeName == "")
+  #if (!$p.kind.primitive && !$p.nullable && ($builderTypeName == "" || !$isFinal))
+    ## We don't need a null check if the type is primitive or @Nullable. We also don't need it
+    ## if there is a builder, since the build() method will check for us. However, if there is a
+    ## builder but there are also extensions (!$isFinal) then we can't omit the null check because
+    ## the constructor is called from the extension code.
 
     if ($p == null) {
       throw new NullPointerException("Null $p.name");
diff --git a/value/src/test/java/com/google/auto/value/processor/CompilationTest.java b/value/src/test/java/com/google/auto/value/processor/CompilationTest.java
index 162f1cf3c6..c5285dd999 100644
--- a/value/src/test/java/com/google/auto/value/processor/CompilationTest.java
+++ b/value/src/test/java/com/google/auto/value/processor/CompilationTest.java
@@ -590,6 +590,7 @@ public void correctBuilder() throws Exception {
         "import com.google.common.base.Optional;",
         "import com.google.common.collect.ImmutableList;",
         "",
+        "import java.util.ArrayList;",
         "import java.util.List;",
         "import javax.annotation.Nullable;",
         "",
@@ -607,21 +608,26 @@ public void correctBuilder() throws Exception {
         "  public abstract Builder<T> toBuilder();",
         "",
         "  @AutoValue.Builder",
-        "  public interface Builder<T extends Number> {",
-        "    Builder<T> anInt(int x);",
-        "    Builder<T> aByteArray(byte[] x);",
-        "    Builder<T> aNullableIntArray(@Nullable int[] x);",
-        "    Builder<T> aList(List<T> x);",
-        "    Builder<T> anImmutableList(List<T> x);",
-        "    ImmutableList.Builder<T> anImmutableListBuilder();",
-        "    Builder<T> anOptionalString(Optional<String> s);",
-        "    Builder<T> anOptionalString(String s);",
+        "  public abstract static class Builder<T extends Number> {",
+        "    public abstract Builder<T> anInt(int x);",
+        "    public abstract Builder<T> aByteArray(byte[] x);",
+        "    public abstract Builder<T> aNullableIntArray(@Nullable int[] x);",
+        "    public abstract Builder<T> aList(List<T> x);",
+        "    public abstract Builder<T> anImmutableList(List<T> x);",
+        "    public abstract ImmutableList.Builder<T> anImmutableListBuilder();",
+        "    public abstract Builder<T> anOptionalString(Optional<String> s);",
+        "    public abstract Builder<T> anOptionalString(String s);",
+        "",
+        "    public Builder<T> aList(ArrayList<T> x) {",
+             // ArrayList should not be imported in the generated class.
+        "      return aList((List<T>) x);",
+        "    }",
         "",
-        "    Optional<Integer> anInt();",
-        "    List<T> aList();",
-        "    ImmutableList<T> anImmutableList();",
+        "    public abstract Optional<Integer> anInt();",
+        "    public abstract List<T> aList();",
+        "    public abstract ImmutableList<T> anImmutableList();",
         "",
-        "    Baz<T> build();",
+        "    public abstract Baz<T> build();",
         "  }",
         "",
         "  public static <T extends Number> Builder<T> builder() {",
@@ -742,7 +748,7 @@ public void correctBuilder() throws Exception {
         "    return new Builder<T>(this);",
         "  }",
         "",
-        "  static final class Builder<T extends Number> implements Baz.Builder<T> {",
+        "  static final class Builder<T extends Number> extends Baz.Builder<T> {",
         "    private Integer anInt;",
         "    private byte[] aByteArray;",
         "    private int[] aNullableIntArray;",
diff --git a/value/userguide/vertical_nav.md b/value/userguide/vertical_nav.md
deleted file mode 100644
index 2e087fdd5c..0000000000
--- a/value/userguide/vertical_nav.md
+++ /dev/null
@@ -1,14 +0,0 @@
-**AutoValue User Guide**
-
-*   [Introduction](index.md)
-    *   [How do I...?](howto.md)
-    *   [Generated example](generated-example.md)
-*   [AutoValue with builders](builders.md)
-    *   [How do I...?](builders-howto.md)
-    *   [Generated example](generated-builder-example.md)
-*   [Extensions](extensions.md)
-*   [Troubleshooting](trouble.md)
-*   [Best practices](practices.md)
-*   [Why AutoValue?](why.md)
-*   [Performance notes](performance.md)
-*   [Design FAQ](design-faq.md)