From 3ad60a8cbbc380d7466cf1fd666e55271be3423f Mon Sep 17 00:00:00 2001
From: Looky1173 <lgl1173and2006@gmail.com>
Date: Sat, 8 Oct 2022 21:51:14 +0200
Subject: [PATCH] Fix #491

---
 src/core/__tests__/compile.test.js | 6 +++---
 src/core/__tests__/parse.test.js   | 5 +++--
 src/core/compile.js                | 2 +-
 src/core/parse.js                  | 2 +-
 4 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/src/core/__tests__/compile.test.js b/src/core/__tests__/compile.test.js
index 1beef589..4d01d9fc 100644
--- a/src/core/__tests__/compile.test.js
+++ b/src/core/__tests__/compile.test.js
@@ -23,9 +23,9 @@ describe('compile', () => {
     });
 
     it('value interpolations', () => {
-        // This interpolations are testing the ability to interpolate thruty and falsy values
+        // This interpolations are testing the ability to interpolate truthy and falsy values
         expect(template`prop: 1; ${() => 0},${() => undefined},${() => null},${2}`({})).toEqual(
-            'prop: 1; 0,,,2'
+            'prop: 1; 0,_,_,2' // '_' represents a falsy value
         );
 
         const tmpl = template`
@@ -39,7 +39,7 @@ describe('compile', () => {
         `;
         expect(tmpl({})).toEqual(`
             background: dodgerblue;
-            
+            _
             border: 1px solid blue;
         `);
     });
diff --git a/src/core/__tests__/parse.test.js b/src/core/__tests__/parse.test.js
index 590b0cda..ea53399c 100644
--- a/src/core/__tests__/parse.test.js
+++ b/src/core/__tests__/parse.test.js
@@ -281,12 +281,13 @@ describe('parse', () => {
                 {
                     div: {
                         opacity: 0,
-                        color: null
+                        color: null,
+                        content: '""'
                     }
                 },
                 ''
             )
-        ).toEqual('div{opacity:0;}');
+        ).toEqual('div{opacity:0;content:"";}');
         expect(
             parse(
                 {
diff --git a/src/core/compile.js b/src/core/compile.js
index 83363d6f..0d016272 100644
--- a/src/core/compile.js
+++ b/src/core/compile.js
@@ -33,7 +33,7 @@ export let compile = (str, defs, data) => {
                 // Here we check if this is strictly a boolean with false value
                 // define it as `''` to be picked up as empty, otherwise use
                 // res value
-                tail = res === false ? '' : res;
+                tail = res === false || res === undefined || res === null ? '_' : res;
             }
         }
         return out + next + (tail == null ? '' : tail);
diff --git a/src/core/parse.js b/src/core/parse.js
index fb05f852..e5cebdb5 100644
--- a/src/core/parse.js
+++ b/src/core/parse.js
@@ -43,7 +43,7 @@ export let parse = (obj, selector) => {
                       })
                     : key
             );
-        } else if (val != undefined) {
+        } else if (val != undefined && val !== '_') {
             // Convert all but CSS variables
             key = /^--/.test(key) ? key : key.replace(/[A-Z]/g, '-$&').toLowerCase();
             // Push the line for this property