Migrate from @CheckForNull to Checker Framework @Nullable.

A future step will migrate from these and our already existing usages of the Checker Framework `@Nullable` to the JSpecify `@Nullable`.

This is the next step toward [using JSpecify in Guava](jspecify/jspecify#239 (comment)).

RELNOTES=Migrated from `@CheckForNull` to Checker Framework `@Nullable`. Most tools recognize both annotations, so we expect this to be a no-op in almost all cases.
PiperOrigin-RevId: 708617636

android/guava-testlib/src/com/google/common/testing/ClassSanityTester.java

@@ -50,7 +50,6 @@
 import java.util.List;
 import java.util.Map.Entry;
 import java.util.Set;
-import javax.annotation.CheckForNull;
 import junit.framework.Assert;
 import junit.framework.AssertionFailedError;
 import org.jspecify.annotations.NullUnmarked;
@@ -657,8 +656,7 @@ private FreshValueGenerator newFreshValueGenerator() {
     FreshValueGenerator generator =
         new FreshValueGenerator() {
           @Override
-          @CheckForNull
-          Object interfaceMethodCalled(Class<?> interfaceType, Method method) {
+          @Nullable Object interfaceMethodCalled(Class<?> interfaceType, Method method) {
             return getDummyValue(TypeToken.of(interfaceType).method(method).getReturnType());
           }
         };
@@ -737,8 +735,7 @@ private List<Object> getDummyArguments(Invokable<?, ?> invokable)
     return args;
   }
 
-  @CheckForNull
-  private <T> T getDummyValue(TypeToken<T> type) {
+  private <T> @Nullable T getDummyValue(TypeToken<T> type) {
     Class<? super T> rawType = type.getRawType();
     @SuppressWarnings("unchecked") // Assume all default values are generics safe.
     T defaultValue = (T) defaultValues.getInstance(rawType);

android/guava-testlib/src/com/google/common/testing/FreshValueGenerator.java

@@ -120,7 +120,6 @@
 import java.util.concurrent.ConcurrentMap;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.regex.Pattern;
-import javax.annotation.CheckForNull;
 import org.jspecify.annotations.NullUnmarked;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
@@ -294,8 +293,8 @@ private final class FreshInvocationHandler extends AbstractInvocationHandler {
     }
 
     @Override
-    @CheckForNull
-    protected Object handleInvocation(Object proxy, Method method, @Nullable Object[] args) {
+    protected @Nullable Object handleInvocation(
+        Object proxy, Method method, @Nullable Object[] args) {
       return interfaceMethodCalled(interfaceType, method);
     }
 
@@ -320,8 +319,7 @@ public String toString() {
   }
 
   /** Subclasses can override to provide different return value for proxied interface methods. */
-  @CheckForNull
-  Object interfaceMethodCalled(Class<?> interfaceType, Method method) {
+  @Nullable Object interfaceMethodCalled(Class<?> interfaceType, Method method) {
     throw new UnsupportedOperationException();
   }
 

android/guava-tests/test/com/google/common/util/concurrent/FuturesGetCheckedInputs.java

@@ -18,8 +18,8 @@
 
 import com.google.common.annotations.GwtCompatible;
 import java.util.concurrent.Future;
-import javax.annotation.CheckForNull;
 import org.jspecify.annotations.NullUnmarked;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * Classes and futures used in {@link FuturesGetCheckedTest} and {@link FuturesGetUncheckedTest}.
@@ -62,7 +62,7 @@ private ExceptionWithPrivateConstructor(String message, Throwable cause) {
   }
 
   public static final class ExceptionWithManyConstructorsButOnlyOneThrowable extends Exception {
-    @CheckForNull private Throwable antecedent;
+    private @Nullable Throwable antecedent;
 
     public ExceptionWithManyConstructorsButOnlyOneThrowable(String message, String a1) {
       super(message);

android/guava/src/com/google/common/base/Absent.java

@@ -19,7 +19,7 @@
 import com.google.common.annotations.GwtCompatible;
 import java.util.Collections;
 import java.util.Set;
-import javax.annotation.CheckForNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /** Implementation of an {@link Optional} not containing a reference. */
 @GwtCompatible
@@ -61,8 +61,7 @@ public T or(Supplier<? extends T> supplier) {
   }
 
   @Override
-  @CheckForNull
-  public T orNull() {
+  public @Nullable T orNull() {
     return null;
   }
 
@@ -78,7 +77,7 @@ public <V> Optional<V> transform(Function<? super T, V> function) {
   }
 
   @Override
-  public boolean equals(@CheckForNull Object object) {
+  public boolean equals(@Nullable Object object) {
     return object == this;
   }
 

android/guava/src/com/google/common/base/AbstractIterator.java

@@ -21,7 +21,6 @@
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import java.util.Iterator;
 import java.util.NoSuchElementException;
-import javax.annotation.CheckForNull;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
@@ -41,14 +40,12 @@ private enum State {
     FAILED,
   }
 
-  @CheckForNull private T next;
+  private @Nullable T next;
 
-  @CheckForNull
-  protected abstract T computeNext();
+  protected abstract @Nullable T computeNext();
 
   @CanIgnoreReturnValue
-  @CheckForNull
-  protected final T endOfData() {
+  protected final @Nullable T endOfData() {
     state = State.DONE;
     return null;
   }

android/guava/src/com/google/common/base/CaseFormat.java

@@ -19,7 +19,7 @@
 
 import com.google.common.annotations.GwtCompatible;
 import java.io.Serializable;
-import javax.annotation.CheckForNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * Utility class for converting between various ASCII case formats. Behavior is undefined for
@@ -181,7 +181,7 @@ protected String doBackward(String s) {
     }
 
     @Override
-    public boolean equals(@CheckForNull Object object) {
+    public boolean equals(@Nullable Object object) {
       if (object instanceof StringConverter) {
         StringConverter that = (StringConverter) object;
         return sourceFormat.equals(that.sourceFormat) && targetFormat.equals(that.targetFormat);

android/guava/src/com/google/common/base/Converter.java

@@ -25,7 +25,7 @@
 import com.google.j2objc.annotations.RetainedWith;
 import java.io.Serializable;
 import java.util.Iterator;
-import javax.annotation.CheckForNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * A function from {@code A} to {@code B} with an associated <i>reverse</i> function from {@code B}
@@ -143,7 +143,7 @@ public abstract class Converter<A, B> implements Function<A, B> {
   private final boolean handleNullAutomatically;
 
   // We lazily cache the reverse view to avoid allocating on every call to reverse().
-  @LazyInit @RetainedWith @CheckForNull private transient Converter<B, A> reverse;
+  @LazyInit @RetainedWith private transient @Nullable Converter<B, A> reverse;
 
   /** Constructor for use by subclasses. */
   protected Converter() {
@@ -189,13 +189,11 @@ protected Converter() {
    *
    * @return the converted value; is null <i>if and only if</i> {@code a} is null
    */
-  @CheckForNull
-  public final B convert(@CheckForNull A a) {
+  public final @Nullable B convert(@Nullable A a) {
     return correctedDoForward(a);
   }
 
-  @CheckForNull
-  B correctedDoForward(@CheckForNull A a) {
+  @Nullable B correctedDoForward(@Nullable A a) {
     if (handleNullAutomatically) {
       // TODO(kevinb): we shouldn't be checking for a null result at runtime. Assert?
       return a == null ? null : checkNotNull(doForward(a));
@@ -204,8 +202,7 @@ B correctedDoForward(@CheckForNull A a) {
     }
   }
 
-  @CheckForNull
-  A correctedDoBackward(@CheckForNull B b) {
+  @Nullable A correctedDoBackward(@Nullable B b) {
     if (handleNullAutomatically) {
       // TODO(kevinb): we shouldn't be checking for a null result at runtime. Assert?
       return b == null ? null : checkNotNull(doBackward(b));
@@ -240,13 +237,11 @@ A correctedDoBackward(@CheckForNull B b) {
    * LegacyConverter does violate the assumptions we make elsewhere.
    */
 
-  @CheckForNull
-  private B unsafeDoForward(@CheckForNull A a) {
+  private @Nullable B unsafeDoForward(@Nullable A a) {
     return doForward(uncheckedCastNullableTToT(a));
   }
 
-  @CheckForNull
-  private A unsafeDoBackward(@CheckForNull B b) {
+  private @Nullable A unsafeDoBackward(@Nullable B b) {
     return doBackward(uncheckedCastNullableTToT(b));
   }
 
@@ -335,14 +330,12 @@ protected B doBackward(A a) {
     }
 
     @Override
-    @CheckForNull
-    A correctedDoForward(@CheckForNull B b) {
+    @Nullable A correctedDoForward(@Nullable B b) {
       return original.correctedDoBackward(b);
     }
 
     @Override
-    @CheckForNull
-    B correctedDoBackward(@CheckForNull A a) {
+    @Nullable B correctedDoBackward(@Nullable A a) {
       return original.correctedDoForward(a);
     }
 
@@ -352,7 +345,7 @@ public Converter<A, B> reverse() {
     }
 
     @Override
-    public boolean equals(@CheckForNull Object object) {
+    public boolean equals(@Nullable Object object) {
       if (object instanceof ReverseConverter) {
         ReverseConverter<?, ?> that = (ReverseConverter<?, ?>) object;
         return this.original.equals(that.original);
@@ -417,19 +410,17 @@ protected A doBackward(C c) {
     }
 
     @Override
-    @CheckForNull
-    C correctedDoForward(@CheckForNull A a) {
+    @Nullable C correctedDoForward(@Nullable A a) {
       return second.correctedDoForward(first.correctedDoForward(a));
     }
 
     @Override
-    @CheckForNull
-    A correctedDoBackward(@CheckForNull C c) {
+    @Nullable A correctedDoBackward(@Nullable C c) {
       return first.correctedDoBackward(second.correctedDoBackward(c));
     }
 
     @Override
-    public boolean equals(@CheckForNull Object object) {
+    public boolean equals(@Nullable Object object) {
       if (object instanceof ConverterComposition) {
         ConverterComposition<?, ?, ?> that = (ConverterComposition<?, ?, ?>) object;
         return this.first.equals(that.first) && this.second.equals(that.second);
@@ -490,7 +481,7 @@ public final B apply(A a) {
    * interchangeable.
    */
   @Override
-  public boolean equals(@CheckForNull Object object) {
+  public boolean equals(@Nullable Object object) {
     return super.equals(object);
   }
 
@@ -539,7 +530,7 @@ protected A doBackward(B b) {
     }
 
     @Override
-    public boolean equals(@CheckForNull Object object) {
+    public boolean equals(@Nullable Object object) {
       if (object instanceof FunctionBasedConverter) {
         FunctionBasedConverter<?, ?> that = (FunctionBasedConverter<?, ?>) object;
         return this.forwardFunction.equals(that.forwardFunction)

android/guava/src/com/google/common/base/Defaults.java

@@ -18,7 +18,7 @@
 
 import com.google.common.annotations.GwtIncompatible;
 import com.google.common.annotations.J2ktIncompatible;
-import javax.annotation.CheckForNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * This class provides default values for all Java types, as defined by the JLS.
@@ -40,8 +40,7 @@ private Defaults() {}
    * {@code void}, {@code null} is returned.
    */
   @SuppressWarnings("unchecked")
-  @CheckForNull
-  public static <T> T defaultValue(Class<T> type) {
+  public static <T> @Nullable T defaultValue(Class<T> type) {
     checkNotNull(type);
     if (type.isPrimitive()) {
       if (type == boolean.class) {

android/guava/src/com/google/common/base/Enums.java

@@ -25,7 +25,7 @@
 import java.util.HashMap;
 import java.util.Map;
 import java.util.WeakHashMap;
-import javax.annotation.CheckForNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * Utility methods for working with {@link Enum} instances.
@@ -132,7 +132,7 @@ protected String doBackward(T enumValue) {
     }
 
     @Override
-    public boolean equals(@CheckForNull Object object) {
+    public boolean equals(@Nullable Object object) {
       if (object instanceof StringConverter) {
         StringConverter<?> that = (StringConverter<?>) object;
         return this.enumClass.equals(that.enumClass);

android/guava/src/com/google/common/base/Equivalence.java

@@ -19,7 +19,6 @@
 import com.google.common.annotations.GwtCompatible;
 import com.google.errorprone.annotations.ForOverride;
 import java.io.Serializable;
-import javax.annotation.CheckForNull;
 import org.checkerframework.checker.nullness.qual.NonNull;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
@@ -65,7 +64,7 @@ protected Equivalence() {}
    * <p>Note that all calls to {@code equivalent(x, y)} are expected to return the same result as
    * long as neither {@code x} nor {@code y} is modified.
    */
-  public final boolean equivalent(@CheckForNull T a, @CheckForNull T b) {
+  public final boolean equivalent(@Nullable T a, @Nullable T b) {
     if (a == b) {
       return true;
     }
@@ -99,7 +98,7 @@ public final boolean equivalent(@CheckForNull T a, @CheckForNull T b) {
    *   <li>{@code hash(null)} is {@code 0}.
    * </ul>
    */
-  public final int hash(@CheckForNull T t) {
+  public final int hash(@Nullable T t) {
     if (t == null) {
       return 0;
     }
@@ -209,7 +208,7 @@ public T get() {
      * equivalence.
      */
     @Override
-    public boolean equals(@CheckForNull Object obj) {
+    public boolean equals(@Nullable Object obj) {
       if (obj == this) {
         return true;
       }
@@ -273,28 +272,28 @@ public String toString() {
    *
    * @since 10.0
    */
-  public final Predicate<@Nullable T> equivalentTo(@CheckForNull T target) {
+  public final Predicate<@Nullable T> equivalentTo(@Nullable T target) {
     return new EquivalentToPredicate<>(this, target);
   }
 
   private static final class EquivalentToPredicate<T>
       implements Predicate<@Nullable T>, Serializable {
 
     private final Equivalence<T> equivalence;
-    @CheckForNull private final T target;
+    private final @Nullable T target;
 
-    EquivalentToPredicate(Equivalence<T> equivalence, @CheckForNull T target) {
+    EquivalentToPredicate(Equivalence<T> equivalence, @Nullable T target) {
       this.equivalence = checkNotNull(equivalence);
       this.target = target;
     }
 
     @Override
-    public boolean apply(@CheckForNull T input) {
+    public boolean apply(@Nullable T input) {
       return equivalence.equivalent(input, target);
     }
 
     @Override
-    public boolean equals(@CheckForNull Object obj) {
+    public boolean equals(@Nullable Object obj) {
       if (this == obj) {
         return true;
       }

android/guava/src/com/google/common/base/FinalizablePhantomReference.java

@@ -18,7 +18,7 @@
 import com.google.common.annotations.J2ktIncompatible;
 import java.lang.ref.PhantomReference;
 import java.lang.ref.ReferenceQueue;
-import javax.annotation.CheckForNull;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * Phantom reference with a {@code finalizeReferent()} method which a background thread invokes
@@ -40,7 +40,7 @@ public abstract class FinalizablePhantomReference<T> extends PhantomReference<T>
    * @param referent to phantom reference
    * @param queue that should finalize the referent
    */
-  protected FinalizablePhantomReference(@CheckForNull T referent, FinalizableReferenceQueue queue) {
+  protected FinalizablePhantomReference(@Nullable T referent, FinalizableReferenceQueue queue) {
     super(referent, queue.queue);
     queue.cleanUp();
   }