New check: ReturnMissingNullable

[jiri-pejchal]

Methods returning null should be annotated @Nullable.

Invalid code:

Date created;
    // failure: missing @Nullable
   public Date getCreated() {
        if (created == null) {
            return null;
        } else {
            return (Date) created.clone();
        }
    }

Valid code:

Date created;
   @Nullable
   public Date getCreated() {
        if (created == null) {
            return null;
        } else {
            return (Date) created.clone();
        }
    }

[rnveach]

@George-007 Are you expecting users to place @NotNull if the method can never return null? If so, please add this as a case to your examples.
Or are you expecting the check to scan the method to look for return null;? This can create false negatives if the return calls another method, especially if the method is in another class/file.

[romani]

Are you expecting users to place @NotNull if the method can never return null?

Checkstyle can not reliably diagnose this, as we do not have type, class hierarchies, and all other meta information about all methods that are in use in method we will validate.

Or are you expecting the check to scan the method to look for return null;?

checkstyle ca not go out of parser file, Check could clearly demand annotation is "return null" is present, But Check will not find complicated cases ... so it should be clearly defined in Check documentation.

[jiri-pejchal]

I'm aware that checkstyle can only parse one file at a time - so only the basic case of returning the null literal from methods if it's possible. The check would be limited. Nevertheless returning null is quite common so it would cover a lot of cases in code.