如何指示方法永远不会使用代码契约返回null？

Optional<String> optionalName = Optional.ofNullable(name);

import com.google.common.base.Preconditions;

public String getName(String name) {
    Preconditions.checkNotNull(name, "Name cannot be null");
    return name;
}

import java.util.Objects;

public String getName(String name) {
    Objects.requireNonNull(name, "Name cannot be null");
    return name;
}

public String getName(String name) {
    assert name != null : "Name cannot be null";
    return name;
}

public String getName(String name) {
    if (name == null) {
        throw new IllegalArgumentException("Name cannot be null");
    }
    return name;
}