@Incubating
class NullChecker
extends TypeCheckingDSL

A compile-time type checker that detects potential null dereferences and null-safety violations in code annotated with @Nullable, @NonNull, and @MonotonicNonNull annotations.

By default, this checker performs annotation-based null checking only. For additional flow-sensitive analysis that tracks nullability through assignments and control flow (even in unannotated code), enable the strict option:

 @TypeChecked(extensions = 'groovy.typecheckers.NullChecker(strict: true)')
 

Supported annotations are recognized by simple name from any package:

• Nullable: @Nullable, @CheckForNull, @MonotonicNonNull
• Non-null: @NonNull, @NotNull, @Nonnull

Detected errors include:

• Assigning null to a @NonNull variable
• Passing null or a @Nullable value to a @NonNull parameter
• Returning null or a @Nullable value from a @NonNull method
• Dereferencing a @Nullable variable without a null check or safe navigation (?.)
• Dereferencing the result of a @Nullable-returning method without a null check
• Re-assigning null to a @MonotonicNonNull field after initialization
• Dereferencing a variable known to be null through flow analysis (strict mode only)

The checker recognizes null guards (if (x != null)), early exit patterns (if (x == null) return/throw), and safe navigation (?.).

 @TypeChecked(extensions = 'groovy.typecheckers.NullChecker')
 void process(@Nullable String input) {
     // input.length()     // error: potential null dereference
     input?.length()       // ok: safe navigation
     if (input != null) {
         input.length()    // ok: null guard
     }
 }