diff --git a/src/components/shared/AuthenticatedImage.tsx b/src/components/shared/AuthenticatedImage.tsx
index 7518d56..bf97227 100644
--- a/src/components/shared/AuthenticatedImage.tsx
+++ b/src/components/shared/AuthenticatedImage.tsx
@@ -1,104 +1,120 @@
-import { useState, useEffect, type ImgHTMLAttributes, type ReactElement } from 'react';
-import { fileService } from '@/services/file-service';
-import apiClient from '@/services/api-client';
-import { Loader2, ImageIcon } from 'lucide-react';
+import {
+  useState,
+  useEffect,
+  type ImgHTMLAttributes,
+  type ReactElement,
+} from "react";
+import { fileService } from "@/services/file-service";
+import apiClient from "@/services/api-client";
+import { Loader2, ImageIcon } from "lucide-react";
 
-interface AuthenticatedImageProps extends Omit<ImgHTMLAttributes<HTMLImageElement>, 'src'> {
-    fileId?: string | null;
-    src?: string | null;
-    fallback?: ReactElement;
+interface AuthenticatedImageProps extends Omit<
+  ImgHTMLAttributes<HTMLImageElement>,
+  "src"
+> {
+  fileId?: string | null;
+  src?: string | null;
+  fallback?: ReactElement;
 }
 
 export const AuthenticatedImage = ({
-    fileId,
-    src,
-    fallback,
-    className,
-    alt = 'Image',
-    ...props
+  fileId,
+  src,
+  fallback,
+  className,
+  alt = "Image",
+  ...props
 }: AuthenticatedImageProps): ReactElement => {
-    const [blobUrl, setBlobUrl] = useState<string | null>(null);
-    const [isLoading, setIsLoading] = useState<boolean>(false);
-    const [error, setError] = useState<boolean>(false);
+  const [blobUrl, setBlobUrl] = useState<string | null>(null);
+  const [isLoading, setIsLoading] = useState<boolean>(false);
+  const [error, setError] = useState<boolean>(false);
 
-    useEffect(() => {
-        // If it's already a blob URL (local preview) or a data URL, use it directly
-        if (src && (src.startsWith('blob:') || src.startsWith('data:'))) {
-            setBlobUrl(src);
+  useEffect(() => {
+    // If it's already a blob URL (local preview) or a data URL, use it directly
+    if (src && (src.startsWith("blob:") || src.startsWith("data:"))) {
+      setBlobUrl(src);
+      return;
+    }
+
+    const baseUrl =
+      import.meta.env.VITE_API_BASE_URL || "http://localhost:3000";
+    const isBackendUrl =
+      src && src.includes(`${baseUrl}/files/`) && src.includes("/preview");
+
+    // If we have a fileId or a backend URL, fetch it via authenticated request
+    if (fileId || isBackendUrl) {
+      let isMounted = true;
+      const fetchImage = async () => {
+        setIsLoading(true);
+        setError(false);
+        try {
+          let url: string;
+          if (fileId) {
+            url = await fileService.getPreview(fileId);
+          } else if (src) {
+            const response = await apiClient.get(src, { responseType: "blob" });
+            url = URL.createObjectURL(response.data);
+          } else {
             return;
+          }
+
+          if (isMounted) {
+            setBlobUrl(url);
+          }
+        } catch (err) {
+          console.error("Failed to fetch authenticated image:", err);
+          if (isMounted) {
+            setError(true);
+          }
+        } finally {
+          if (isMounted) {
+            setIsLoading(false);
+          }
         }
+      };
 
-        const baseUrl = import.meta.env.VITE_API_BASE_URL || 'http://localhost:3000';
-        const isBackendUrl = src && src.includes(`${baseUrl}/files/`) && src.includes('/preview');
+      fetchImage();
 
-        // If we have a fileId or a backend URL, fetch it via authenticated request
-        if (fileId || isBackendUrl) {
-            let isMounted = true;
-            const fetchImage = async () => {
-                setIsLoading(true);
-                setError(false);
-                try {
-                    let url: string;
-                    if (fileId) {
-                        url = await fileService.getPreview(fileId);
-                    } else if (src) {
-                        const response = await apiClient.get(src, { responseType: 'blob' });
-                        url = URL.createObjectURL(response.data);
-                    } else {
-                        return;
-                    }
-
-                    if (isMounted) {
-                        setBlobUrl(url);
-                    }
-                } catch (err) {
-                    console.error('Failed to fetch authenticated image:', err);
-                    if (isMounted) {
-                        setError(true);
-                    }
-                } finally {
-                    if (isMounted) {
-                        setIsLoading(false);
-                    }
-                }
-            };
-
-            fetchImage();
-
-            return () => {
-                isMounted = false;
-                if (blobUrl && blobUrl.startsWith('blob:')) {
-                    URL.revokeObjectURL(blobUrl);
-                }
-            };
-        } else if (src) {
-            // For other external URLs, use them directly
-            setBlobUrl(src);
+      return () => {
+        isMounted = false;
+        if (blobUrl && blobUrl.startsWith("blob:")) {
+          URL.revokeObjectURL(blobUrl);
         }
-    }, [fileId, src]);
-
-    if (isLoading) {
-        return (
-            <div className={`flex items-center justify-center bg-[#f5f7fa] rounded-md ${className}`}>
-                <Loader2 className="w-5 h-5 text-[#6b7280] animate-spin" />
-            </div>
-        );
-    }
-
-    if (error || (!blobUrl && !src)) {
-        return fallback || (
-            <div className={`flex items-center justify-center bg-[#f5f7fa] rounded-md ${className}`}>
-                <ImageIcon className="w-5 h-5 text-[#9ca3af]" />
-            </div>
-        );
+      };
+    } else if (src) {
+      // For other external URLs, use them directly
+      setBlobUrl(src);
     }
+  }, [fileId, src]);
 
+  if (isLoading) {
     return (
-        <img
-            src={blobUrl || src || ''}
-            className={className}
-            alt={alt}
-            {...props}
-        />
+      <div
+        className={`flex items-center justify-center bg-[#f5f7fa] rounded-md ${className}`}
+      >
+        <Loader2 className="w-5 h-5 text-[#6b7280] animate-spin" />
+      </div>
     );
+  }
+
+  if (error || (!blobUrl && !src)) {
+    return (
+      fallback || (
+        <div
+          className={`flex items-center justify-center bg-[#f5f7fa] rounded-md ${className}`}
+        >
+          <ImageIcon className="w-5 h-5 text-[#9ca3af]" />
+        </div>
+      )
+    );
+  }
+
+  return (
+    <img
+      src={blobUrl || src || ""}
+      className={className}
+      alt={alt}
+      {...props}
+    />
+  );
 };
diff --git a/src/components/shared/EditUserModal.tsx b/src/components/shared/EditUserModal.tsx
index 6130219..1d5d73b 100644
--- a/src/components/shared/EditUserModal.tsx
+++ b/src/components/shared/EditUserModal.tsx
@@ -345,6 +345,17 @@ export const EditUserModal = ({
       if (defaultTenantId) {
         data.tenant_id = defaultTenantId;
       }
+      // Normalize empty strings to null for optional UUID fields
+      if (!data.department_id) data.department_id = undefined;
+      if (!data.designation_id) data.designation_id = undefined;
+      
+      // If category is tenant_user, supplier_id should always be null
+      if (data.category === "tenant_user") {
+        data.supplier_id = null;
+      } else if (!data.supplier_id) {
+        data.supplier_id = null;
+      }
+      
       await onSubmit(userId, data);
     } catch (error: any) {
       if (
@@ -491,13 +502,13 @@ export const EditUserModal = ({
                   { value: "supplier_user", label: "Supplier User" },
                 ]}
                 value={categoryValue || "tenant_user"}
-                onValueChange={(value) =>
-                  setValue(
-                    "category",
-                    value as "tenant_user" | "supplier_user",
-                    { shouldValidate: true },
-                  )
-                }
+                onValueChange={(value) => {
+                  const category = value as "tenant_user" | "supplier_user";
+                  setValue("category", category, { shouldValidate: true });
+                  if (category === "tenant_user") {
+                    setValue("supplier_id", null);
+                  }
+                }}
                 error={errors.category?.message}
               />
 
diff --git a/src/components/shared/NewUserModal.tsx b/src/components/shared/NewUserModal.tsx
index 5e5b4bd..59e6a92 100644
--- a/src/components/shared/NewUserModal.tsx
+++ b/src/components/shared/NewUserModal.tsx
@@ -216,6 +216,17 @@ export const NewUserModal = ({
     clearErrors();
     try {
       const { confirmPassword, ...submitData } = data;
+      // Normalize empty strings to null for optional UUID fields
+      if (!submitData.department_id) submitData.department_id = undefined;
+      if (!submitData.designation_id) submitData.designation_id = undefined;
+      
+      // If category is tenant_user, supplier_id should always be null
+      if (submitData.category === "tenant_user") {
+        submitData.supplier_id = null;
+      } else if (!submitData.supplier_id) {
+        submitData.supplier_id = null;
+      }
+      
       await onSubmit(submitData);
     } catch (error: any) {
       // Handle validation errors from API
@@ -387,11 +398,13 @@ export const NewUserModal = ({
                 { value: "supplier_user", label: "Supplier User" },
               ]}
               value={categoryValue || "tenant_user"}
-              onValueChange={(value) =>
-                setValue("category", value as "tenant_user" | "supplier_user", {
-                  shouldValidate: true,
-                })
-              }
+                onValueChange={(value) => {
+                  const category = value as "tenant_user" | "supplier_user";
+                  setValue("category", category, { shouldValidate: true });
+                  if (category === "tenant_user") {
+                    setValue("supplier_id", null);
+                  }
+                }}
               error={errors.category?.message}
             />