Add MUST as native for NON NULL behavior

src/core/n-control.c

@@ -575,6 +575,27 @@ REBNATIVE(match_p)
 }
 
 
+//
+//  must: native [
+//
+//  {Ensure that the argument is not NULL}
+//
+//      return: "Same as input value if non-NULL"
+//          [any-value!]
+//      value [<opt> any-value!]
+//  ]
+//
+REBNATIVE(must)  // `must x` is a faster synonym for `non null x`
+{
+    INCLUDE_PARAMS_OF_MUST;
+
+    if (IS_NULLED(ARG(value)))
+        fail ("MUST requires argument to not be NULL");
+
+    RETURN (ARG(value));
+}
+
+
 //
 //  all: native [
 //

tests/control/match.test.reb

@@ -105,6 +105,13 @@
 ]
 
 
+; MUST is an optimized form of NON NULL
+[
+    ("bc" = must find "abc" "b")
+    (error? trap [must find "abc" "q"])
+]
+
+
 ; MATCH was an early function for trying a REFRAMER-like capacity for
 ; building a frame of an invocation, stealing its first argument, and then
 ; returning that in the case of a match.  But now that REFRAMER exists,