Fix an issue with builder getters.

In a builder, if a property `bar` has its own builder `barBuilder()` and also a getter `bar()`, then either the property must be set or `barBuilder()` must be called.
If neither of those has happened, both the `bar` and `barBuilder$` fields will be null, and we should correctly report that with an empty `Optional` return from `bar()`.
Previously we incorrectly simplified this logic and ended up calling `Optional.of(bar)` even though `bar` is null.

Fixes #1386. Thanks to @jmesny for the bug report and regression test.

RELNOTES=Fixed an issue when a builder has a property `foo` with both a getter `foo()` and a builder `fooBuilder()`.
PiperOrigin-RevId: 483736037

Author: eamonnmcmanus

value/src/it/functional/src/test/java/com/google/auto/value/AutoValueJava8Test.java

@@ -42,6 +42,7 @@
 import java.util.Arrays;
 import java.util.List;
 import java.util.Optional;
+import java.util.OptionalDouble;
 import java.util.Set;
 import java.util.function.Predicate;
 import javax.annotation.processing.AbstractProcessor;
@@ -862,4 +863,63 @@ public void testOptionalExtends() {
     OptionalExtends t = OptionalExtends.builder().setPredicate(predicate).build();
     assertThat(t.predicate()).hasValue(predicate);
   }
+
+  @AutoValue
+  public abstract static class Foo {
+    public abstract Bar bar();
+
+    public abstract double baz();
+
+    public static Foo.Builder builder() {
+      return new AutoValue_AutoValueJava8Test_Foo.Builder();
+    }
+
+    @AutoValue.Builder
+    public abstract static class Builder {
+      // https://github.com/google/auto/blob/master/value/userguide/builders-howto.md#normalize
+      abstract Optional<Bar> bar();
+
+      public abstract Builder bar(Bar bar);
+
+      // https://github.com/google/auto/blob/master/value/userguide/builders-howto.md#nested_builders
+      public abstract Bar.Builder barBuilder();
+
+      abstract OptionalDouble baz();
+
+      public abstract Builder baz(double baz);
+
+      abstract Foo autoBuild();
+
+      public Foo build() {
+        if (!bar().isPresent()) {
+          bar(Bar.builder().build());
+        }
+        if (!baz().isPresent()) {
+          baz(0.0);
+        }
+        return autoBuild();
+      }
+    }
+  }
+
+  @AutoValue
+  public abstract static class Bar {
+    public abstract Bar.Builder toBuilder();
+
+    public static Bar.Builder builder() {
+      return new AutoValue_AutoValueJava8Test_Bar.Builder();
+    }
+
+    @AutoValue.Builder
+    public abstract static class Builder {
+      public abstract Bar build();
+    }
+  }
+
+  @Test
+  public void nestedOptionalGetter() {
+    Foo foo = Foo.builder().build();
+    assertThat(foo.bar()).isNotNull();
+    assertThat(foo.baz()).isEqualTo(0.0);
+  }
 }

value/src/main/java/com/google/auto/value/processor/builder.vm

@@ -192,7 +192,7 @@ class ${builderName}${builderFormalTypes} ##
     if ($noValueToGetCondition) {
       return $builderGetter.optional.empty;
     }
-      #elseif ($p.nullable)
+      #else
     if ($p == null) {
       return $builderGetter.optional.empty;
     }