diff --git a/example/env.yml b/example/env.yml
index 9b387b8..f6e45f2 100644
--- a/example/env.yml
+++ b/example/env.yml
@@ -1,16 +1,14 @@
 default_env: &default_env
   IA_ENV: ${env:IA_ENV}
-  FOO: ${cft:forms-api-fargate-stack.ServiceURL}
   BAZ: BAR
-  CRED: ${cred:IA_VPC_PRIVATE_SUBNET1_ID}
-  CRED_OPTIONAL: 
-    value: ${cred:IDSFJKLJ}
-    optional: true
   TEST: ${poop:hello}
   INTEGER_VALUE: 3000
   BOOLEAN_TRUE_VALUE: true
   BOOLEAN_FALSE_VALUE: false
-  VALUE_WITH_SURROUNDING_STRINGS: test-${IA_ENV}-test
+  VALUE_WITH_SURROUNDING_STRINGS: test-${env:IA_ENV}-test
+  OPTIONAL_VALUE:
+    value: ${env:IA_OPTIONAL}
+    optional: true
 
 sandbox:
   <<: *default_env
diff --git a/package.json b/package.json
index 6ba8b8b..7440d54 100644
--- a/package.json
+++ b/package.json
@@ -11,7 +11,8 @@
     "build": "yarn tsc",
     "test": "yarn jest",
     "precommit": "lint-staged",
-    "release": "semantic-release"
+    "release": "semantic-release",
+    "example": "pushd example && IA_ENV=test node ../dist/index.js -f env.yml -s development && popd"
   },
   "bin": {
     "dotenvi": "dist/index.js"
diff --git a/src/rewriter.test.js b/src/rewriter.test.js
index 60c1d98..63d9ee9 100644
--- a/src/rewriter.test.js
+++ b/src/rewriter.test.js
@@ -76,4 +76,18 @@ describe('Rewriter', () => {
       expect(output['test']).toBe('footestbartest-test');
     });
   });
+
+  it('Supports optionals', () => {
+    const document = {
+      test: {
+        value: '${env:OPTIONAL}',
+        optional: true
+      }
+    };
+
+    const rewriter = new Rewriter({ resolvers: resolvers });
+    return rewriter.rewrite(document).then(output => {
+      expect(output['test']).toBe('');
+    });
+  });
 });
diff --git a/src/rewriter.ts b/src/rewriter.ts
index 8064e92..be43849 100644
--- a/src/rewriter.ts
+++ b/src/rewriter.ts
@@ -1,4 +1,5 @@
 import { Document, InputDocument, Config, Primitive } from './types';
+import { isNullOrUndefined } from 'util';
 
 export class Rewriter {
   constructor(private config: Config) {}
@@ -31,12 +32,12 @@ export class Rewriter {
           if (!resolver) {
             throw new Error(`Could not locate resolver for value ${value}`);
           }
-          const innerValue = matchResults ? matchResults[2] : value;
-          let innerResult = await resolver(innerValue, this.config);
-          if (!innerResult) {
-            throw new Error(`Resolver ${resolverName} didn't return any value`);
+          const argument = matchResults ? matchResults[2] : value;
+          let resolved = await resolver(argument, this.config);
+          const rewrittenValue = await this.rewriteValue(resolved);
+          if (!isNullOrUndefined(rewrittenValue)) {
+            result += rewrittenValue;
           }
-          result += await this.rewriteValue(innerResult);
           capture = '';
         } else if (capture) {
           capture += c;
diff --git a/src/utils.ts b/src/utils.ts
index 27a2eeb..c11321c 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -25,7 +25,7 @@ export function validateOutput(input: InputDocument, output: Document): string[]
   const keys = Object.keys(input);
   for (const key of keys) {
     if (!input[key].optional) {
-      if (!(key in output) || output[key] === undefined) {
+      if (!(key in output) || output[key] === undefined || output[key] === '') {
         errors.push(`${key} is a required variable but is not specified in result`);
       }
     }