diff --git a/adminforth/modules/configValidator.ts b/adminforth/modules/configValidator.ts
index 0e5d31891..148180f5e 100644
--- a/adminforth/modules/configValidator.ts
+++ b/adminforth/modules/configValidator.ts
@@ -530,7 +530,6 @@ export default class ConfigValidator implements IConfigValidator {
         }
 
         if (col.foreignResource) {
-
           if (!col.foreignResource.resourceId) {
             // resourceId is absent or empty
             if (!col.foreignResource.polymorphicResources && !col.foreignResource.polymorphicOn) {
@@ -550,11 +549,11 @@ export default class ConfigValidator implements IConfigValidator {
               }
               // we do || here because 'resourceId' might yet not be assigned from 'table'
               col.foreignResource.polymorphicResources.forEach((polymorphicResource, polymorphicResourceIndex) => {
-                if (!polymorphicResource.resourceId) {
+                if (polymorphicResource.resourceId === undefined) {
                   errors.push(`Resource "${res.resourceId}" column "${col.name}" has polymorphic foreign resource without resourceId`);
                 } else if (!polymorphicResource.whenValue) {
                   errors.push(`Resource "${res.resourceId}" column "${col.name}" has polymorphic foreign resource without whenValue`);
-                } else {
+                } else if (polymorphicResource.resourceId !== null) {
                   const resource = this.inputConfig.resources.find((r) => r.resourceId === polymorphicResource.resourceId || r.table === polymorphicResource.resourceId);
                   if (!resource) {
                     const similar = suggestIfTypo(this.inputConfig.resources.map((r) => r.resourceId || r.table), polymorphicResource.resourceId);
diff --git a/adminforth/modules/restApi.ts b/adminforth/modules/restApi.ts
index 8486e5353..0ec1f5b64 100644
--- a/adminforth/modules/restApi.ts
+++ b/adminforth/modules/restApi.ts
@@ -703,7 +703,14 @@ export default class AdminForthRestAPI implements IAdminForthRestAPI {
               const targetResourcePkFields = {};
               const pksUniques = {};
               col.foreignResource.polymorphicResources.forEach((pr) => {
-                targetResources[pr.whenValue] = this.adminforth.config.resources.find((res) => res.resourceId == pr.resourceId);
+                if (pr.resourceId === null) {
+                  return;
+                }
+                const targetResource = this.adminforth.config.resources.find((res) => res.resourceId == pr.resourceId);
+                if (!targetResource) {
+                  return;
+                }
+                targetResources[pr.whenValue] = targetResource;
                 targetConnectors[pr.whenValue] = this.adminforth.connectors[targetResources[pr.whenValue].dataSource];
                 targetResourcePkFields[pr.whenValue] = targetResources[pr.whenValue].columns.find((col) => col.primaryKey).name;
                 const pksUnique = [...new Set(data.data.filter((item) => item[col.foreignResource.polymorphicOn] === pr.whenValue).map((item) => item[col.name]))];
@@ -747,6 +754,13 @@ export default class AdminForthRestAPI implements IAdminForthRestAPI {
             
             data.data.forEach((item) => {
               item[col.name] = targetDataMap[item[col.name]];
+              
+              if (!item[col.name]) {
+                const systemResource = col.foreignResource.polymorphicResources.find(pr => pr.resourceId === null);
+                if (systemResource) {
+                  item[col.foreignResource.polymorphicOn] = systemResource.whenValue;
+                }
+              }
             });
           })
         );
@@ -819,7 +833,7 @@ export default class AdminForthRestAPI implements IAdminForthRestAPI {
           return { error: `Column '${column}' in resource '${resourceId}' is not a foreign key` };
         }
 
-        const targetResourceIds = columnConfig.foreignResource.resourceId ? [columnConfig.foreignResource.resourceId] : columnConfig.foreignResource.polymorphicResources.map((pr) => pr.resourceId);
+        const targetResourceIds = columnConfig.foreignResource.resourceId ? [columnConfig.foreignResource.resourceId] : columnConfig.foreignResource.polymorphicResources.filter(pr => pr.resourceId !== null).map((pr) => pr.resourceId);
         const targetResources = targetResourceIds.map((trId) => this.adminforth.config.resources.find((res) => res.resourceId == trId));
 
         const responses = (await Promise.all(
@@ -974,7 +988,14 @@ export default class AdminForthRestAPI implements IAdminForthRestAPI {
                 const targetConnectors = {};
                 const targetResourcePkFields = {};
                 column.foreignResource.polymorphicResources.forEach((pr) => {
-                  targetResources[pr.whenValue] = this.adminforth.config.resources.find((res) => res.resourceId == pr.resourceId);
+                  if (pr.resourceId === null) {
+                    return;
+                  }
+                  const targetResource = this.adminforth.config.resources.find((res) => res.resourceId == pr.resourceId);
+                  if (!targetResource) {
+                    return;
+                  }
+                  targetResources[pr.whenValue] = targetResource;
                   targetConnectors[pr.whenValue] = this.adminforth.connectors[targetResources[pr.whenValue].dataSource];
                   targetResourcePkFields[pr.whenValue] = targetResources[pr.whenValue].columns.find((col) => col.primaryKey).name;
                 });
@@ -1062,7 +1083,14 @@ export default class AdminForthRestAPI implements IAdminForthRestAPI {
                   const targetConnectors = {};
                   const targetResourcePkFields = {};
                   column.foreignResource.polymorphicResources.forEach((pr) => {
-                    targetResources[pr.whenValue] = this.adminforth.config.resources.find((res) => res.resourceId == pr.resourceId);
+                    if (pr.resourceId === null) {
+                      return;
+                    }
+                    const targetResource = this.adminforth.config.resources.find((res) => res.resourceId == pr.resourceId);
+                    if (!targetResource) {
+                      return;
+                    }
+                    targetResources[pr.whenValue] = targetResource;
                     targetConnectors[pr.whenValue] = this.adminforth.connectors[targetResources[pr.whenValue].dataSource];
                     targetResourcePkFields[pr.whenValue] = targetResources[pr.whenValue].columns.find((col) => col.primaryKey).name;
                   });
diff --git a/dev-demo/resources/api_keys.ts b/dev-demo/resources/api_keys.ts
index cd055ae8b..429896c81 100644
--- a/dev-demo/resources/api_keys.ts
+++ b/dev-demo/resources/api_keys.ts
@@ -54,6 +54,10 @@ export default {
             resourceId: 'providers',
             whenValue: 'provider',
           },
+          {
+            resourceId: null,
+            whenValue: 'Syst1em',
+          },
         ],
         polymorphicOn: 'owner',
       },