Minor improvement to error handling wrt exception propagating via Creator (esp. for NPEs and other no-message exception types)

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/DeserializationContext.java

@@ -1589,15 +1589,21 @@ public JsonMappingException weirdNativeValueException(Object value, Class<?> ins
      * to indicate problem with physically constructing instance of
      * specified class (missing constructor, exception from constructor)
      *<p>
-     * Note that most of the time this method should NOT be called; instead,
+     * Note that most of the time this method should NOT be called directly; instead,
      * {@link #handleInstantiationProblem} should be called which will call this method
      * if necessary.
      */
     public JsonMappingException instantiationException(Class<?> instClass, Throwable cause) {
         // Most likely problem with Creator definition, right?
-        JavaType type = constructType(instClass);
+        final JavaType type = constructType(instClass);
+        String excMsg;
+        if (cause == null) {
+            excMsg = "N/A";
+        } else if ((excMsg = cause.getMessage()) == null) {
+            excMsg = ClassUtil.nameOf(cause.getClass());
+        }
         String msg = String.format("Cannot construct instance of %s, problem: %s",
-                ClassUtil.nameOf(instClass), cause.getMessage());
+                ClassUtil.nameOf(instClass), excMsg);
         InvalidDefinitionException e = InvalidDefinitionException.from(_parser, msg, type);
         e.initCause(cause);
         return e;