diff --git a/ufc/flags-v1-obfuscated.json b/ufc/flags-v1-obfuscated.json
index 2d2f119..193722e 100644
--- a/ufc/flags-v1-obfuscated.json
+++ b/ufc/flags-v1-obfuscated.json
@@ -608,6 +608,70 @@
         }
       ]
     },
+    "aca57f6611d05b7ac7fe76a60220101d": {
+      "key": "aca57f6611d05b7ac7fe76a60220101d",
+      "enabled": true,
+      "variationType": "BOOLEAN",
+      "totalShards": 10000,
+      "variations": {
+        "ZGlzYWJsZWQ=": {
+          "key": "ZGlzYWJsZWQ=",
+          "value": "ZmFsc2U="
+        },
+        "ZW5hYmxlZA==": {
+          "key": "ZW5hYmxlZA==",
+          "value": "dHJ1ZQ=="
+        }
+      },
+      "allocations": [
+        {
+          "key": "ZGlzYWJsZS1mb3ItYW5vbnltb3Vz",
+          "doLog": true,
+          "rules": [
+            {
+              "conditions": [
+                {
+                  "operator": "27457ce369f2a74203396a35ef537c0b",
+                  "attribute": "d7b5164029f944313b08c6b778b7b178",
+                  "value": [
+                    "294de3557d9d00b3d2d8a1e6aab028cf"
+                  ]
+                }
+              ]
+            }
+          ],
+          "splits": [
+            {
+              "variationKey": "ZGlzYWJsZWQ=",
+              "shards": []
+            }
+          ]
+        },
+        {
+          "key": "ZW5hYmxlLWZvci11c2Vycw==",
+          "doLog": true,
+          "rules": [
+            {
+              "conditions": [
+                {
+                  "operator": "27457ce369f2a74203396a35ef537c0b",
+                  "attribute": "d7b5164029f944313b08c6b778b7b178",
+                  "value": [
+                    "a2b8ed9c305b8ea86116b603cca78a97"
+                  ]
+                }
+              ]
+            }
+          ],
+          "splits": [
+            {
+              "variationKey": "ZW5hYmxlZA==",
+              "shards": []
+            }
+          ]
+        }
+      ]
+    },
     "ea55330f6cbbaf8f57556df645c037e2": {
       "key": "ea55330f6cbbaf8f57556df645c037e2",
       "enabled": true,
diff --git a/ufc/flags-v1.json b/ufc/flags-v1.json
index b882934..1419869 100644
--- a/ufc/flags-v1.json
+++ b/ufc/flags-v1.json
@@ -609,6 +609,70 @@
       ],
       "totalShards": 10000
     },
+    "empty-string-subject-key-flag": {
+      "key": "empty-string-subject-key-flag",
+      "enabled": true,
+      "variationType": "BOOLEAN",
+      "variations": {
+        "disabled": {
+          "key": "disabled",
+          "value": false
+        },
+        "enabled": {
+          "key": "enabled",
+          "value": true
+        }
+      },
+      "allocations": [
+        {
+          "key": "disable-for-anonymous",
+          "rules": [
+            {
+              "conditions": [
+                {
+                  "attribute": "user_type",
+                  "operator": "ONE_OF",
+                  "value": [
+                    "anonymous"
+                  ]
+                }
+              ]
+            }
+          ],
+          "splits": [
+            {
+              "variationKey": "disabled",
+              "shards": []
+            }
+          ],
+          "doLog": true
+        },
+        {
+          "key": "enable-for-users",
+          "rules": [
+            {
+              "conditions": [
+                {
+                  "attribute": "user_type",
+                  "operator": "ONE_OF",
+                  "value": [
+                    "registered"
+                  ]
+                }
+              ]
+            }
+          ],
+          "splits": [
+            {
+              "variationKey": "enabled",
+              "shards": []
+            }
+          ],
+          "doLog": true
+        }
+      ],
+      "totalShards": 10000
+    },
     "kill-switch": {
       "key": "kill-switch",
       "enabled": true,
diff --git a/ufc/tests/test-case-empty-string-subject-key.json b/ufc/tests/test-case-empty-string-subject-key.json
new file mode 100644
index 0000000..7c77834
--- /dev/null
+++ b/ufc/tests/test-case-empty-string-subject-key.json
@@ -0,0 +1,109 @@
+{
+  "flag": "empty-string-subject-key-flag",
+  "variationType": "BOOLEAN",
+  "defaultValue": true,
+  "subjects": [
+    {
+      "subjectKey": "",
+      "subjectAttributes": {
+        "user_type": "anonymous"
+      },
+      "assignment": true,
+      "evaluationDetails": {
+        "environmentName": "Test",
+        "flagEvaluationCode": "DEFAULT_ALLOCATION_NULL",
+        "flagEvaluationDescription": "Empty subject key provided. Falling back to \"Default Allocation\", serving NULL",
+        "banditKey": null,
+        "banditAction": null,
+        "variationKey": null,
+        "variationValue": null,
+        "matchedRule": null,
+        "matchedAllocation": null,
+        "unmatchedAllocations": [
+          {
+            "key": "disable-for-anonymous",
+            "allocationEvaluationCode": "UNEVALUATED",
+            "orderPosition": 1
+          },
+          {
+            "key": "enable-for-users",
+            "allocationEvaluationCode": "UNEVALUATED",
+            "orderPosition": 2
+          }
+        ],
+        "unevaluatedAllocations": []
+      }
+    },
+    {
+      "subjectKey": "user123",
+      "subjectAttributes": {
+        "user_type": "registered"
+      },
+      "assignment": true,
+      "evaluationDetails": {
+        "environmentName": "Test",
+        "flagEvaluationCode": "MATCH",
+        "flagEvaluationDescription": "Supplied attributes match rules defined in allocation \"enable-for-users\".",
+        "banditKey": null,
+        "banditAction": null,
+        "variationKey": "enabled",
+        "variationValue": true,
+        "matchedRule": {
+          "conditions": [
+            {
+              "attribute": "user_type",
+              "operator": "ONE_OF",
+              "value": [
+                "registered"
+              ]
+            }
+          ]
+        },
+        "matchedAllocation": {
+          "key": "enable-for-users",
+          "allocationEvaluationCode": "MATCH",
+          "orderPosition": 2
+        },
+        "unmatchedAllocations": [
+          {
+            "key": "disable-for-anonymous",
+            "allocationEvaluationCode": "FAILING_RULE",
+            "orderPosition": 1
+          }
+        ],
+        "unevaluatedAllocations": []
+      }
+    },
+    {
+      "subjectKey": "guest_user",
+      "subjectAttributes": {
+        "user_type": "unknown"
+      },
+      "assignment": true,
+      "evaluationDetails": {
+        "environmentName": "Test",
+        "flagEvaluationCode": "DEFAULT_ALLOCATION_NULL",
+        "flagEvaluationDescription": "No allocations matched. Falling back to \"Default Allocation\", serving NULL",
+        "banditKey": null,
+        "banditAction": null,
+        "variationKey": null,
+        "variationValue": null,
+        "matchedRule": null,
+        "matchedAllocation": null,
+        "unmatchedAllocations": [
+          {
+            "key": "disable-for-anonymous",
+            "allocationEvaluationCode": "FAILING_RULE",
+            "orderPosition": 1
+          },
+          {
+            "key": "enable-for-users",
+            "allocationEvaluationCode": "FAILING_RULE",
+            "orderPosition": 2
+          }
+        ],
+        "unevaluatedAllocations": []
+      }
+    }
+  ]
+}
\ No newline at end of file