add is_nil operator

Author: LeandroSNunes

querybuilder/operator/is_nil.go

@@ -0,0 +1,16 @@
+package operator
+
+func init() {
+	AddOperator(IsNil)
+}
+
+var IsNil = &Operator{
+	Name: "is_nil",
+	Evaluate: func(input, value interface{}) bool {
+		if input == nil {
+			return true
+		}
+
+		return false
+	},
+}

querybuilder/operator/is_nil_test.go

@@ -0,0 +1,28 @@
+package operator
+
+import "testing"
+
+func TestIsNil(t *testing.T) {
+	var typeNil interface{}
+
+	var inputs = []struct {
+		title string
+		value interface{}
+		input interface{}
+		want  bool
+	}{
+		{title: "is_nil-1", value: nil, input: "", want: false},
+		{title: "is_nil-2", value: nil, input: typeNil, want: true},
+		{title: "is_nil-3", value: nil, input: []int{}, want: false},
+		{title: "is_nil-5", value: nil, input: nil, want: true},
+	}
+
+	for _, input := range inputs {
+		t.Run(input.title, func(t *testing.T) {
+			got := IsNil.Evaluate(input.input, input.value)
+			if got != input.want {
+				t.Errorf("%v is nil %v got: %t, want: %t", input.input, input.value, got, input.want)
+			}
+		})
+	}
+}