diff --git a/src/fs/json2env.test.ts b/src/fs/json2env.test.ts
new file mode 100644
index 0000000..d906bae
--- /dev/null
+++ b/src/fs/json2env.test.ts
@@ -0,0 +1,39 @@
+import { objectToGithubActionsEnv, objectToShellExport } from './json2env'
+
+test('objectToGithubActionsEnv', () => {
+  expect(objectToGithubActionsEnv({})).toBe('')
+
+  expect(
+    objectToGithubActionsEnv({
+      a: 'a',
+      minInstances: 0,
+      maxInstances: 8,
+      c: false,
+      d: true,
+    }),
+  ).toMatchInlineSnapshot(`
+"a=a
+minInstances=0
+maxInstances=8
+c=false
+d=true
+"
+`)
+
+  expect(
+    objectToShellExport({
+      a: 'a',
+      minInstances: 0,
+      maxInstances: 8,
+      c: false,
+      d: true,
+    }),
+  ).toMatchInlineSnapshot(`
+"export a="a"
+export minInstances="0"
+export maxInstances="8"
+export c="false"
+export d="true"
+"
+`)
+})
diff --git a/src/fs/json2env.ts b/src/fs/json2env.ts
index e1ceec5..1c34f7a 100644
--- a/src/fs/json2env.ts
+++ b/src/fs/json2env.ts
@@ -148,7 +148,7 @@ export function objectToShellExport(obj: AnyObject, prefix = ''): string {
   return (
     Object.entries(obj)
       .map(([k, v]) => {
-        if (v) {
+        if (v !== undefined && v !== null) {
           return `export ${prefix}${k}="${v}"`
         }
       })
@@ -179,7 +179,7 @@ export function objectToGithubActionsEnv(obj: AnyObject, prefix = ''): string {
   return (
     Object.entries(obj)
       .map(([k, v]) => {
-        if (v) {
+        if (v !== undefined && v !== null) {
           return `${prefix}${k}=${v}`
         }
       })