Fix OSS-Fuzz found issue with null for "suppressable" entries for Throwables (#4261)

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/deser/std/ThrowableDeserializer.java

@@ -208,7 +208,10 @@ public Object deserializeFromObject(JsonParser p, DeserializationContext ctxt) t
         // any suppressed exceptions?
         if (suppressed != null) {
             for (Throwable s : suppressed) {
-                throwable.addSuppressed(s);
+                // 13-Dec-2023, tatu: But skip any `null` entries we might have gotten
+                if (s != null) {
+                    throwable.addSuppressed(s);
+                }
             }
         }
 

src/test/java/com/fasterxml/jackson/databind/exc/ExceptionDeserializationTest.java

@@ -298,4 +298,13 @@ public void testWithDups() throws Exception
         assertNotNull(exc);
         assertEquals("foo", exc.getLocalizedMessage());
     }
+
+    // Found by OSS-Fuzz: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=65042
+    public void testWithNullSuppressed() throws Exception
+    {
+        final String json = a2q("{'message': 'Message!', 'suppressed':[null]}");
+        IOException exc = MAPPER.readValue(json, IOException.class);
+        assertNotNull(exc);
+        assertEquals("Message!", exc.getMessage());
+    }
 }