### Question:
InternalQueries { @NonNull public static String nonNullString(@Nullable String str) { return str == null ? "" : str; } private  InternalQueries(); @NonNull static List<String> unmodifiableNonNullListOfStrings(@Nullable Object[] args); @NonNull static List<String> unmodifiableNonNullListOfStrings(@Nullable List<?> args); @NonNull static List<Object> unmodifiableNonNullList(@Nullable Object[] args); @SuppressWarnings("unchecked") @NonNull static List<T> unmodifiableNonNullList(@Nullable List<T> list); @SuppressWarnings("unchecked") @NonNull static Set<T> unmodifiableNonNullSet(@Nullable Set<T> set); @NonNull static String[] nonNullArrayOfStrings(@Nullable List<String> list); @Nullable static String[] nullableArrayOfStringsFromListOfStrings(@Nullable List<String> list); @Nullable static String[] nullableArrayOfStrings(@Nullable List<Object> list); @NonNull static String nonNullString(@Nullable String str); @Nullable static String nullableString(@Nullable String str); @SuppressWarnings("unchecked") @NonNull static Set<String> nonNullSet(@Nullable Collection<String> collection); @SuppressWarnings("unchecked") @NonNull static Set<String> nonNullSet(@Nullable String[] items); @SuppressWarnings("unchecked") @NonNull static Set<String> nonNullSet(@NonNull String firstItem, @Nullable String[] otherItems);  }### Answer:
@Test public void nonNullStringFromNull() { assertThat(InternalQueries.nonNullString(null)).isEqualTo(""); }
@Test public void nonNullStringFromEmptyString() { assertThat(InternalQueries.nonNullString("")).isEqualTo(""); }
@Test public void nonNullStringFromNormalString() { assertThat(InternalQueries.nonNullString("123")).isEqualTo("123"); }