diff --git a/parser_test.go b/parser_test.go
index afd81bd..30e22a8 100644
--- a/parser_test.go
+++ b/parser_test.go
@@ -64,7 +64,7 @@ func TestParser(t *testing.T) {
 		/*  43 */ {`+false`, nil, errors.New(`[1:2] prefix/postfix operator "+" do not support operand 'false' [bool]`)},
 		/*  44 */ {`false // very simple expression`, false, nil},
 		/*  45 */ {`1 + // Missing right operator`, nil, errors.New(`[1:4] infix operator "+" requires two non-nil operands, got 1`)},
-		/*  46 */ {"", nil, errors.New(`empty expression`)},
+		/*  46 */ {"", nil, nil},
 		/*  47 */ {"4!", int64(24), nil},
 		/*  48 */ {"(-4)!", nil, errors.New(`factorial of a negative integer (-4) is not allowed`)},
 		/*  49 */ {"-4!", int64(-24), nil},
@@ -158,6 +158,9 @@ func TestParser(t *testing.T) {
 		/* 137 */ {`2 + 1 ? {"a"} : {"b"} * 3`, "2bbb", nil},
 		/* 138 */ {`nil`, nil, nil},
 		/* 139 */ {`null`, nil, errors.New(`undefined variable "null"`)},
+		/* 140 */ {`isNil(nil)`, true, nil},
+		/* 141 */ {`v=nil; isNil(v)`, true, nil},
+		/* 142 */ {`v=5; isNil(v)`, false, nil},
 	}
 	check_env_expr_path := 113
 
@@ -165,7 +168,7 @@ func TestParser(t *testing.T) {
 	failed := 0
 
 	// inputs1 := []inputType{
-	// 	{`10 ? {"a"} :[true, 2+8] {"b"} :: {"c"}`, "b", nil},
+	// 	/* 140 */ {`isNil(nil)`, true, nil},
 	// }
 
 	for i, input := range inputs {