public @Nullable V put(@ParametricNullness K key, @ParametricNullness V value) {
      checkArgument(apply(key, value));
      return unfiltered.put(key, value);
    }

    @Override
    public void putAll(Map<? extends K, ? extends V> map) {
      for (Entry<? extends K, ? extends V> entry : map.entrySet()) {
        checkArgument(apply(entry.getKey(), entry.getValue()));
      }
      unfiltered.putAll(map);
    }

    public @Nullable V put(@ParametricNullness K key, @ParametricNullness V value) {
      checkArgument(apply(key, value));
      return unfiltered.put(key, value);
    }

    @Override
    public void putAll(Map<? extends K, ? extends V> map) {
      for (Entry<? extends K, ? extends V> entry : map.entrySet()) {
        checkArgument(apply(entry.getKey(), entry.getValue()));
      }
      unfiltered.putAll(map);
    }

package com.google.common.util.concurrent;

import static com.google.common.base.Functions.constant;
import static com.google.common.base.MoreObjects.toStringHelper;
import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static com.google.common.base.Throwables.throwIfUnchecked;