Non-nullity: equals/hashCode/toString throws NullPointerExcpetion

This error occurs when the class under test can throw a NullPointerException when one of its fields is null and equals/hashCode/toString is called. For example, equals could contain this line:

return foo.equals(other.foo);

It will throw a NullPointerException if foo is null. This can be avoided in three ways:

  • In Java 7 and up, you can use Objects.equals, which is null-safe:
return Objects.equals(foo, other.foo);
  • You can add a null check, like so:
return foo == null ? other.foo == null : foo.equals(other.foo);
  • If you’re certain the field can never be null (for instance, because the class’s constructor explicitly checks for it), you can add .withNonnullFields("foo") to your call to EqualsVerifier

  • If this problem occurs for many fields in the same class, you can suppress Warning.NULL_FIELDS in your call to EqualsVerifier.

You can read more about dealing with null in the manual page about null.