throw error instead of panic when replacements source.fieldPath doesn't exist (#4166)

* test for missing source.fieldPath in replacements

* throw error instead of panic when replacements source.fieldPath doesn't exist

api/filters/replacement/replacement.go

@@ -131,10 +131,11 @@ func getReplacement(nodes []*yaml.RNode, r *types.Replacement) (*yaml.RNode, err
 	if err != nil {
 		return nil, err
 	}
-	if !rn.IsNilOrEmpty() {
-		return getRefinedValue(r.Source.Options, rn)
+	if rn.IsNilOrEmpty() {
+		return nil, fmt.Errorf("fieldPath `%s` is missing for replacement source %s", r.Source.FieldPath, r.Source)
 	}
-	return rn, nil
+
+	return getRefinedValue(r.Source.Options, rn)
 }
 
 func getRefinedValue(options *types.FieldOptions, rn *yaml.RNode) (*yaml.RNode, error) {

api/filters/replacement/replacement_test.go

@@ -1556,6 +1556,38 @@ spec:
         name: postgresdb
 `,
 		},
+
+		"replacement source.fieldPath does not exist": {
+			input: `apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: ports-from
+data:
+  grpcPort: 8080
+---
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: ports-to
+data:
+  grpcPort: 8081
+`,
+			replacements: `replacements:
+- source:
+    kind: ConfigMap
+    name: ports-from
+    fieldPath: data.httpPort
+  targets:
+  - select:
+      kind: ConfigMap
+      name: ports-to
+    fieldPaths:
+    - data.grpcPort
+    options:
+      create: true
+`,
+			expectedErr: "fieldPath `data.httpPort` is missing for replacement source ~G_~V_ConfigMap|~X|ports-from:data.httpPort",
+		},
 	}
 
 	for tn, tc := range testCases {