fix(jsonpath): Prevent panic when body is "null"

Resolves #718

core/condition_test.go

@@ -259,6 +259,27 @@ func TestCondition_evaluate(t *testing.T) {
 			ExpectedSuccess: true,
 			ExpectedOutput:  "[BODY][0].id == 1",
 		},
+		{
+			Name:            "body-jsonpath-when-body-has-null-parameter",
+			Condition:       Condition("[BODY].data == OK"),
+			Result:          &Result{Body: []byte(`{"data": null}"`)},
+			ExpectedSuccess: false,
+			ExpectedOutput:  "[BODY].data (INVALID) == OK",
+		},
+		{
+			Name:            "body-jsonpath-when-body-has-array-with-null",
+			Condition:       Condition("[BODY].items[0] == OK"),
+			Result:          &Result{Body: []byte(`{"items": [null, null]}"`)},
+			ExpectedSuccess: false,
+			ExpectedOutput:  "[BODY].items[0] (INVALID) == OK",
+		},
+		{
+			Name:            "body-jsonpath-when-body-is-null",
+			Condition:       Condition("[BODY].data == OK"),
+			Result:          &Result{Body: []byte(`null`)},
+			ExpectedSuccess: false,
+			ExpectedOutput:  "[BODY].data (INVALID) == OK",
+		},
 		{
 			Name:            "body-jsonpath-when-body-is-array-but-actual-body-is-not",
 			Condition:       Condition("[BODY][0].name == test"),

jsonpath/jsonpath.go

@@ -117,8 +117,15 @@ func extractValue(currentKey string, value interface{}) interface{} {
 	}
 	if valueAsSlice, ok := value.([]interface{}); ok {
 		// If the type is a slice, return it
+		// This happens when the body (value) is a JSON array
 		return valueAsSlice
 	}
-	// otherwise, it's a map
-	return value.(map[string]interface{})[currentKey]
+	if valueAsMap, ok := value.(map[string]interface{}); ok {
+		// If the value is a map, then we get the currentKey from that map
+		// This happens when the body (value) is a JSON object
+		return valueAsMap[currentKey]
+	}
+	// If the value is neither a map, nor a slice, nor an index, then we cannot retrieve the currentKey
+	// from said value. This usually happens when the body (value) is null.
+	return value
 }