Improve now() and date() validation

Author: antonmedv

builtin/builtin.go

@@ -487,7 +487,7 @@ var Builtins = []*Function{
 				return timeType, nil
 			}
 			if len(args) == 1 {
-				if args[0].AssignableTo(locationType) {
+				if args[0] != nil && args[0].AssignableTo(locationType) {
 					return timeType, nil
 				}
 			}
@@ -559,7 +559,7 @@ var Builtins = []*Function{
 			if len(args) < 1 {
 				return anyType, fmt.Errorf("invalid number of arguments (expected at least 1, got %d)", len(args))
 			}
-			if args[0].AssignableTo(locationType) {
+			if args[0] != nil && args[0].AssignableTo(locationType) {
 				args = args[1:]
 			}
 			if len(args) > 3 {

builtin/builtin_test.go

@@ -233,6 +233,9 @@ func TestBuiltin_errors(t *testing.T) {
 		{`bitshr(-5, -2)`, "invalid operation: negative shift count -2 (type int) (1:1)"},
 		{`bitshl(1, -1)`, "invalid operation: negative shift count -1 (type int) (1:1)"},
 		{`bitushr(-5, -2)`, "invalid operation: negative shift count -2 (type int) (1:1)"},
+		{`now(nil)`, "invalid number of arguments (expected 0, got 1)"},
+		{`date(nil)`, "interface {} is nil, not string (1:1)"},
+		{`timezone(nil)`, "interface {} is nil, not string (1:1)"},
 	}
 	for _, test := range errorTests {
 		t.Run(test.input, func(t *testing.T) {