Reword message a bit more based on review feedback

Author: tbkka

stdlib/public/runtime/DynamicCast.cpp

@@ -126,8 +126,8 @@ static HeapObject * getNonNullSrcObject(OpaqueValue *srcValue,
 
   std::string srcTypeName = nameForMetadata(srcType);
   std::string destTypeName = nameForMetadata(destType);
-  const char * const msg = "Non-Optional value of type '%s' (%p)"
-                    " holds a null pointer?!"
+  const char * const msg = "Found a null pointer in a value of type '%s' (%p)."
+                    " Non-Optional values are not allowed to hold null pointers."
                     " (Detected while casting to '%s' (%p))%s\n";
   if (runtime::bincompat::useLegacyPermissiveObjCNullSemanticsInCasting()) {
     // In backwards compatibility mode, this code will warn and return the null

test/Casting/CastTraps.swift.gyb

@@ -107,9 +107,8 @@ CastTrapsTestSuite.test("${t1}__${t2}")
 protocol P2 {}
 if #available(SwiftStdlib 5.5, *) {
 CastTrapsTestSuite.test("Unexpected null")
-  .crashOutputMatches("Non-Optional value of type '")
+  .crashOutputMatches("Found a null pointer in a value of type '")
   .crashOutputMatches("Foo'")
-  .crashOutputMatches("holds a null pointer")
   .crashOutputMatches("(Detected while casting to '")
   .crashOutputMatches("P2'")
   .code
@@ -128,8 +127,7 @@ CastTrapsTestSuite.test("Unexpected null")
 #if _runtime(_ObjC)
 if #available(SwiftStdlib 5.5, *) {
 CastTrapsTestSuite.test("Unexpected Obj-C null")
-  .crashOutputMatches("Non-Optional value of type 'NSObject'")
-  .crashOutputMatches("holds a null pointer")
+  .crashOutputMatches("Found a null pointer in a value of type 'NSObject'")
   .crashOutputMatches("(Detected while casting to '")
   .crashOutputMatches("P2'")
   .code