Sonarqube说：可能会抛出“ NullPointerException”。 “ getFolderPath（）”可以返回null

Question

I get a following bug from sonarqube

A "NullPointerException" could be thrown; "getFolderPath()" can return null.

for the following line:

if (upstreamContent.getFolderPath() != null && !upstreamContent.getFolderPath().isEmpty()) {
   ...
}

Where upstreamContent may not be null.

How can I fix it in sonarqube without turning off the rule?

UPDATE:

Someone asked me to show the source of UpstreamContent

public class UpstreamContent {

    @Nullable
    private String folderPath;

    ...

    @CheckForNull
    @Nullable
    public String getFolderPath() {
        return folderPath;
    }

    public void setFolderPath(String folderPath) {
        this.folderPath = folderPath;
    }
}

Answer 1

Probably by saving the result to a variable rather than making the call twice:

String path = upstreamContent.getFolderPath();
if (path != null && !path.isEmpty()) {
   ...
}

Maybe you or I know that if it doesn't return null the first time, it won't the second (I don't, actually, because I don't know what upstreamContent is :-) ), but a general-purpose tool can't know or assume that. For all it knows, it could return non- null the first time and null the second. By saving the call result to a variable, we ensure that Sonarqube and anyone coming along later to read and maintain the code knows, for sure, that we've done a null check before calling isEmpty .

In fact, now that you've posted the code for upstreamContent 's class, it's entirely possible for getFolderPath to return non- null for the first call and null for the second (if another thread calls setFolderPath(null) in-between).