http://findbugs.sourceforge.net/: Annotation the FindBugs tool supports 
package javax.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

import javax.annotation.meta.TypeQualifierDefault;


This annotation can be applied to a package, class or method to indicate that
the method parameters in that element are nullable by default unless there is:

    

  • An explicit nullness annotation

  • The method overrides a method in a superclass (in which case the
annotation of the corresponding parameter in the superclass applies)

  •  there is a default parameter annotation applied to a more tightly nested
element.



This annotation implies the same "nullness" as no annotation. However, it is different
than having no annotation, as it is inherited and it can override a ParametersAreNonnullByDefault
annotation at an outer scope.

/**
 * This annotation can be applied to a package, class or method to indicate that
 * the method parameters in that element are nullable by default unless there is:
 * <ul>
 * <li>An explicit nullness annotation
 * <li>The method overrides a method in a superclass (in which case the
 * annotation of the corresponding parameter in the superclass applies)
 * <li> there is a default parameter annotation applied to a more tightly nested
 * element.
 * </ul>
 * <p>This annotation implies the same "nullness" as no annotation. However, it is different
 * than having no annotation, as it is inherited and it can override a ParametersAreNonnullByDefault
 * annotation at an outer scope.
 * 
 */
@Documented
@Nullable
@TypeQualifierDefault(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
public @interface ParametersAreNullableByDefault {
}