From 5586c0423d38014bbbc99b1579e75db7faca9153 Mon Sep 17 00:00:00 2001
From: Samsondeen Dare <samsondeen.dare@hashicorp.com>
Date: Mon, 10 Mar 2025 08:27:46 +0000
Subject: [PATCH 1/3] backport of commit
 10ddb3b3ff2d99124769f0160c9356819c10d0b4

---
 internal/lang/funcs/string.go      |  8 ++++++++
 internal/lang/funcs/string_test.go | 22 ++++++++++++++++++++++
 2 files changed, 30 insertions(+)

diff --git a/internal/lang/funcs/string.go b/internal/lang/funcs/string.go
index c026bb9508ca..932c36da774f 100644
--- a/internal/lang/funcs/string.go
+++ b/internal/lang/funcs/string.go
@@ -380,6 +380,14 @@ func makeRenderTemplateFunc(funcsCb func() (funcs map[string]function.Function,
 		if diags.HasErrors() {
 			return cty.DynamicVal, diags
 		}
+		if val.IsNull() {
+			return cty.DynamicVal, &hcl.Diagnostic{
+				Severity: hcl.DiagError,
+				Summary:  "Template result is null",
+				Detail:   "The result of the template is null, which is not a valid result for a templatestring call.",
+				Subject:  expr.Range().Ptr(),
+			}
+		}
 		return val, nil
 	}
 }
diff --git a/internal/lang/funcs/string_test.go b/internal/lang/funcs/string_test.go
index 19f2f7f13823..83b602aa1583 100644
--- a/internal/lang/funcs/string_test.go
+++ b/internal/lang/funcs/string_test.go
@@ -273,6 +273,28 @@ func TestTemplateString(t *testing.T) {
 		want         cty.Value
 		wantErr      string
 	}{
+		{ // a single string interpolation that evaluates to null should fail
+			`template`,
+			map[string]cty.Value{
+				"template": cty.StringVal(`${test}`),
+			},
+			cty.ObjectVal(map[string]cty.Value{
+				"test": cty.NullVal(cty.String),
+			}),
+			cty.NilVal,
+			`<templatestring argument>:1,1-8: Template result is null; The result of the template is null, which is not a valid result for a templatestring call.`,
+		},
+		{ // a single string interpolation that evaluates to unknown should not fail
+			`template`,
+			map[string]cty.Value{
+				"template": cty.StringVal(`${test}`),
+			},
+			cty.ObjectVal(map[string]cty.Value{
+				"test": cty.UnknownVal(cty.String),
+			}),
+			cty.UnknownVal(cty.String).RefineNotNull(),
+			``,
+		},
 		{
 			`template`,
 			map[string]cty.Value{

From 94186aedcd356a046cafc6611190c44b422e6657 Mon Sep 17 00:00:00 2001
From: Samsondeen Dare <samsondeen.dare@hashicorp.com>
Date: Mon, 10 Mar 2025 08:32:02 +0000
Subject: [PATCH 2/3] backport of commit
 031fb73f5f94054f36e6d94b68889c8ae6666b7a

---
 .changes/v1.12/BUG FIXES-20250310-093153.yaml | 5 +++++
 1 file changed, 5 insertions(+)
 create mode 100644 .changes/v1.12/BUG FIXES-20250310-093153.yaml

diff --git a/.changes/v1.12/BUG FIXES-20250310-093153.yaml b/.changes/v1.12/BUG FIXES-20250310-093153.yaml
new file mode 100644
index 000000000000..8b69b58c0bcb
--- /dev/null
+++ b/.changes/v1.12/BUG FIXES-20250310-093153.yaml	
@@ -0,0 +1,5 @@
+kind: BUG FIXES
+body: Return error when the template's single interpolation results in null value
+time: 2025-03-10T09:31:53.479704+01:00
+custom:
+    Issue: "36652"

From b8124cb85d87d2153392bbc841a4d0e379fafa01 Mon Sep 17 00:00:00 2001
From: Samsondeen <40821565+dsa0x@users.noreply.github.com>
Date: Mon, 10 Mar 2025 11:24:25 +0000
Subject: [PATCH 3/3] backport of commit
 774192b2919e55854491c5b1458de05b47f87e5b

---
 .changes/v1.12/BUG FIXES-20250310-093153.yaml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/.changes/v1.12/BUG FIXES-20250310-093153.yaml b/.changes/v1.12/BUG FIXES-20250310-093153.yaml
index 8b69b58c0bcb..de9f86c6a3ac 100644
--- a/.changes/v1.12/BUG FIXES-20250310-093153.yaml	
+++ b/.changes/v1.12/BUG FIXES-20250310-093153.yaml	
@@ -1,5 +1,5 @@
 kind: BUG FIXES
-body: Return error when the template's single interpolation results in null value
+body: Return error when the templatestring function contains only a single interpolation that evaluates to a null value
 time: 2025-03-10T09:31:53.479704+01:00
 custom:
     Issue: "36652"