import org.checkerframework.checker.nullness.qual.EnsuresNonNullIf;
import org.checkerframework.checker.nullness.qual.NonNull;
import org.checkerframework.checker.nullness.qual.Nullable;

package com.google.common.base;

class Strings {
  @EnsuresNonNullIf(result = false, expression = "#1")
  static boolean isNullOrEmpty(@Nullable String str);
}

class Preconditions {
  static <T extends @NonNull Object> T checkNotNull(T reference, @Nullable Object errorMessage);
}