A DESCRIPTION OF THE PROBLEM :
If the custom implementation of equals() of any of AbstractSet members throws NullPointerException, it is silently ignored and false is returned instead. It happens because AbstractSet#equals ignores both NullPointerException and ClassCastException when containsAll() is invoked to compare each member of this set with another set and returns false instead.

As per JavaDoc, AbstractSet#containsAll() may throw NullPointerException "if the specified collection contains one or more null elements and this collection does not permit null elements (optional), or if the specified collection is null." But what if containsAll() encounters member's equals() implementation that throws NullPointerException? How does this imply that two sets are not equal? I see how ignoring ClassCastException makes sense - comparing two objects that produce such an exception already implies that they are not equal in the OOP world (you can compare Cat to Animal and Animal to Cat, but can't compare Cat to Dog) and therefore makes containsAll() return false, because one set may contain a Dog and another a Cat. But why would NullPointerException return false? It may as well indicate a programming error instead of a comparison with null element of a collection or null collection, for example, a null pointer dereference during the comparison of object fields implemented in equals() of the set's member (these fields may or may not be actually equal). In this case, we can't know for certain if the sets are not equal, because the result of the comparison is unknown as it couldn't continue due to the developer's fault. Thus we should crash and wait for the developer to interfere.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Run the source code attached
2. Observe no NullPointerException thrown

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
NullPointerException is thrown
ACTUAL -
No NullPointerException is thrown

---------- BEGIN SOURCE ----------
public class Pojo {
public String attr;

public Pojo(String attr) {
this.attr = attr;
}

public static Pojo of(String attr) {
return new Pojo(attr);
}

@Override
public boolean equals(Object o) {
System.out.println("Pojo.equals() is called!");
throw new NullPointerException();
}

@Override
public int hashCode() {
return Objects.hash(attr);
}
}

Pojo p1 = Pojo.of("Hello");
Pojo p2 = Pojo.of("Hello");

Set<Pojo> set1 = new HashSet<>();
Set<Pojo> set2 = new HashSet<>();
set1.add(p1);
set2.add(p2);

set1.equals(set2);
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Wrap NullPointerException in RuntimeException