diff --git a/.github/workflows/lambda.yml b/.github/workflows/lambda.yml
index 626c2f4..9053d93 100644
--- a/.github/workflows/lambda.yml
+++ b/.github/workflows/lambda.yml
@@ -10,6 +10,14 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
+      - name: Get GitHub Commit SHA based on Ref
+        id: commit
+        run: |
+          if [[ '${{ github.ref }}' == 'refs/heads/master' ]]; then
+              echo "::set-output name=sha::${{ github.sha }}"
+          else
+              echo "::set-output name=sha::${{ github.event.pull_request.head.sha }}"
+          fi
       # Checkout the pull request branch
       - name: Checkout code
         uses: actions/checkout@v2
@@ -30,10 +38,10 @@ jobs:
         run: make build
 
       - name: Deploy
-        run: aws s3 cp --acl public-read artifacts/lambda.zip s3://artifacts.prod.cloudposse.org/${{ github.event.repository.name }}/${{ github.sha }}/lambda.zip
+        run: aws s3 cp --acl public-read artifacts/lambda.zip s3://artifacts.prod.cloudposse.org/${{ github.event.repository.name }}/${{ steps.commit.outputs.sha }}/lambda.zip
         env:
           AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
           AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
 
       - name: Test Download from CDN
-        run: curl -fsSL -o /dev/null https://artifacts.cloudposse.com/${{ github.event.repository.name }}/${{ github.sha }}/lambda.zip
+        run: curl -fsSL -o /dev/null https://artifacts.cloudposse.com/${{ github.event.repository.name }}/${{ steps.commit.outputs.sha }}/lambda.zip
diff --git a/README.md b/README.md
index a7059db..567a34a 100644
--- a/README.md
+++ b/README.md
@@ -167,7 +167,7 @@ is given
 | Name | Description | Type | Default | Required |
 |------|-------------|------|---------|:--------:|
 | additional\_tag\_map | Additional tags for appending to tags\_as\_list\_of\_maps. Not added to `tags`. | `map(string)` | `{}` | no |
-| artifact\_git\_ref | Git ref of the lambda artifact to use. Use latest version if null. | `string` | `null` | no |
+| artifact\_git\_ref | Git ref of the lambda artifact to use. Use latest version if null. | `string` | `""` | no |
 | artifact\_url | URL template for the remote artifact | `string` | `"https://artifacts.cloudposse.com/$${module_name}/$${git_ref}/$${filename}"` | no |
 | attributes | Additional attributes (e.g. `1`) | `list(string)` | `[]` | no |
 | context | Single object for setting entire context at once.<br>See description of individual variables for details.<br>Leave string and numeric variables as `null` to use default value.<br>Individual variable settings (non-null) override settings in context object,<br>except for attributes, tags, and additional\_tag\_map, which are merged. | <pre>object({<br>    enabled             = bool<br>    namespace           = string<br>    environment         = string<br>    stage               = string<br>    name                = string<br>    delimiter           = string<br>    attributes          = list(string)<br>    tags                = map(string)<br>    additional_tag_map  = map(string)<br>    regex_replace_chars = string<br>    label_order         = list(string)<br>    id_length_limit     = number<br>  })</pre> | <pre>{<br>  "additional_tag_map": {},<br>  "attributes": [],<br>  "delimiter": null,<br>  "enabled": true,<br>  "environment": null,<br>  "id_length_limit": null,<br>  "label_order": [],<br>  "name": null,<br>  "namespace": null,<br>  "regex_replace_chars": null,<br>  "stage": null,<br>  "tags": {}<br>}</pre> | no |
diff --git a/docs/terraform.md b/docs/terraform.md
index 784f48b..1614cf0 100644
--- a/docs/terraform.md
+++ b/docs/terraform.md
@@ -25,7 +25,7 @@ is given
 | Name | Description | Type | Default | Required |
 |------|-------------|------|---------|:--------:|
 | additional\_tag\_map | Additional tags for appending to tags\_as\_list\_of\_maps. Not added to `tags`. | `map(string)` | `{}` | no |
-| artifact\_git\_ref | Git ref of the lambda artifact to use. Use latest version if null. | `string` | `null` | no |
+| artifact\_git\_ref | Git ref of the lambda artifact to use. Use latest version if null. | `string` | `""` | no |
 | artifact\_url | URL template for the remote artifact | `string` | `"https://artifacts.cloudposse.com/$${module_name}/$${git_ref}/$${filename}"` | no |
 | attributes | Additional attributes (e.g. `1`) | `list(string)` | `[]` | no |
 | context | Single object for setting entire context at once.<br>See description of individual variables for details.<br>Leave string and numeric variables as `null` to use default value.<br>Individual variable settings (non-null) override settings in context object,<br>except for attributes, tags, and additional\_tag\_map, which are merged. | <pre>object({<br>    enabled             = bool<br>    namespace           = string<br>    environment         = string<br>    stage               = string<br>    name                = string<br>    delimiter           = string<br>    attributes          = list(string)<br>    tags                = map(string)<br>    additional_tag_map  = map(string)<br>    regex_replace_chars = string<br>    label_order         = list(string)<br>    id_length_limit     = number<br>  })</pre> | <pre>{<br>  "additional_tag_map": {},<br>  "attributes": [],<br>  "delimiter": null,<br>  "enabled": true,<br>  "environment": null,<br>  "id_length_limit": null,<br>  "label_order": [],<br>  "name": null,<br>  "namespace": null,<br>  "regex_replace_chars": null,<br>  "stage": null,<br>  "tags": {}<br>}</pre> | no |
diff --git a/variables.tf b/variables.tf
index 7a97b54..8b177ac 100644
--- a/variables.tf
+++ b/variables.tf
@@ -86,6 +86,6 @@ variable "artifact_url" {
 variable "artifact_git_ref" {
   type        = string
   description = "Git ref of the lambda artifact to use. Use latest version if null."
-  default     = null
+  default     = ""
 }