diff --git a/R/db_startup.R b/R/db_startup.R
index 4daa3b0..f74737c 100644
--- a/R/db_startup.R
+++ b/R/db_startup.R
@@ -222,7 +222,7 @@ CREATE TABLE if not exists segments (
   "users" = "
 CREATE TABLE if not exists users (
     user_id INTEGER PRIMARY KEY
-,   user_login TEXT UNIQUE
+,   user_login TEXT UNIQUE NOT NULL
 ,   user_name TEXT
 ,   user_mail TEXT
 ,   created_at TEXT DEFAULT CURRENT_TIMESTAMP
diff --git a/R/mod_user_manager.R b/R/mod_user_manager.R
index 7b600ce..8e9265e 100644
--- a/R/mod_user_manager.R
+++ b/R/mod_user_manager.R
@@ -1,5 +1,10 @@
-utils::globalVariables(c("user_id_copy", "permission", "project_admin", 
-                         "permissions_modify", "project_owner"))
+utils::globalVariables(c(
+  "user_id_copy",
+  "permission",
+  "project_admin",
+  "permissions_modify",
+  "project_owner"
+))
 
 #' user_manager UI Function
 #'
@@ -14,31 +19,37 @@ mod_user_manager_ui <- function(id) {
   ns <- NS(id)
   tagList(
     if (golem::get_golem_options("mode") == "server") {
-      fluidRow(class = "module_tools",
-      mod_rql_button_ui(ns("add_user_ui"),
-        label = "Add user",
-        icon = "plus",
-        inputId = ns("add_menu")
-      ),
-      mod_rql_button_ui(ns("remove_user_ui"),
-        label = "Remove user",
-        icon = "minus",
-        inputId = ns("remove_menu")
-      ),
-      mod_rql_button_ui(ns("modify_permissions_ui"),
-        label = "Modify permissions",
-        icon = "lock",
-        inputId = ns("modify_permissions")
+      fluidRow(
+        class = "module_tools",
+        mod_rql_button_ui(
+          ns("add_user_ui"),
+          label = "Add user",
+          icon = "plus",
+          inputId = ns("add_menu")
+        ),
+        mod_rql_button_ui(
+          ns("remove_user_ui"),
+          label = "Remove user",
+          icon = "minus",
+          inputId = ns("remove_menu")
+        ),
+        mod_rql_button_ui(
+          ns("modify_permissions_ui"),
+          label = "Modify permissions",
+          icon = "lock",
+          inputId = ns("modify_permissions")
+        )
       )
-      ) 
     },
-    fluidRow(class = "module_content",
-      tags$h2("Project members"), tags$br(),
+    fluidRow(
+      class = "module_content",
+      tags$h2("Project members"),
+      tags$br(),
       DT::DTOutput(ns("assigned_users")),
       if (golem::get_golem_options("mode") == "local") {
         "User management is only enabled for the server version."
       }
-  )
+    )
   )
 }
 
@@ -55,11 +66,18 @@ mod_user_manager_server <- function(id, glob) {
       if (golem::get_golem_options("mode") == "server") {
         # on init, get a list of users in credentials
         loc$all_users <- get_users(
-          credentials_path = golem::get_golem_options(which = "credentials_path"),
-          credentials_pass = golem::get_golem_options(which = "credentials_pass")
+          credentials_path = golem::get_golem_options(
+            which = "credentials_path"
+          ),
+          credentials_pass = golem::get_golem_options(
+            which = "credentials_pass"
+          )
         )
 
-        loc$all_users_choices <- stats::setNames(loc$all_users$user_id, loc$all_users$user_login)
+        loc$all_users_choices <- stats::setNames(
+          loc$all_users$user_id,
+          loc$all_users$user_login
+        )
 
         loc$users_permissions_df <- get_user_permissions(
           glob$pool,
@@ -74,16 +92,15 @@ mod_user_manager_server <- function(id, glob) {
 
     # render project members =======================================================
     output$assigned_users <- DT::renderDataTable(server = FALSE, {
-      req(golem::get_golem_options("mode") == "server") 
+      req(golem::get_golem_options("mode") == "server")
 
-        loc$users_display <- loc$users_permissions_df %>%
+      loc$users_display <- loc$users_permissions_df %>%
         transform_user_table()
-          
-  
+
       DT::datatable(
-      loc$users_display,
-      escape = FALSE, # To allow the rendering of HTML elements
-      rownames = FALSE
+        loc$users_display,
+        escape = FALSE, # To allow the rendering of HTML elements
+        rownames = FALSE
       )
     })
 
@@ -94,23 +111,32 @@ mod_user_manager_server <- function(id, glob) {
         "Missing permission to modify permissions."
       )
       req(input$members_permissions)
-      
+
       modified_permissions_df <- loc$users_permissions_df %>%
-      dplyr::filter(user_id %in% input$members_permissions) %>%
-      dplyr::mutate(dplyr::across(dplyr::matches("modify|view"), .fns = function(x) {
-        x  <- 0 # reset permissions
-      })) %>%
-      dplyr::mutate(dplyr::across(dplyr::all_of(input$permissions_list), .fns = function(x) {
-        x  <- 1 # apply new permissions
-      }))
+        dplyr::filter(!is.na(user_login)) %>%
+        dplyr::filter(user_id %in% input$members_permissions) %>%
+        dplyr::mutate(dplyr::across(
+          dplyr::matches("modify|view"),
+          .fns = function(x) {
+            x <- 0 # reset permissions
+          }
+        )) %>%
+        dplyr::mutate(dplyr::across(
+          dplyr::all_of(input$permissions_list),
+          .fns = function(x) {
+            x <- 1 # apply new permissions
+          }
+        ))
 
       # Enforce that project owner can always modify permission
-      modified_permissions_df$permissions_modify[modified_permissions_df$project_owner == 1] <- 1
-      
+      modified_permissions_df$permissions_modify[
+        modified_permissions_df$project_owner == 1
+      ] <- 1
+
       modify_permissions_record(
         pool = glob$pool,
         project_id = glob$active_project,
-        permissions_df = modified_permissions_df, 
+        permissions_df = modified_permissions_df,
         user_id = glob$user$user_id
       )
       loc$users_permissions_df <- get_user_permissions(
@@ -132,17 +158,24 @@ mod_user_manager_server <- function(id, glob) {
       existing_users <- dplyr::tbl(glob$pool, "users") %>%
         dplyr::pull(user_id)
 
-      existing_users_check <- input$rql_users[!input$rql_users %in% existing_users]
+      existing_users_check <- input$rql_users[
+        !input$rql_users %in% existing_users
+      ]
 
       if (length(existing_users_check) > 0) {
         # create user in db if an uknown user is assigned
         users_df <- loc$all_users %>%
-          dplyr::filter(user_id %in% as.integer(input$rql_users))
+          dplyr::filter(user_id %in% as.integer(input$rql_users)) %>%
+          dplyr::filter(!is.na(user_login))
         purrr::map(users_df$user_id, .f = function(x) {
           users_df_filtered <- users_df %>%
             dplyr::filter(user_id == as.integer(x))
-          DBI::dbWriteTable(glob$pool, "users", users_df_filtered,
-            append = TRUE, row.names = FALSE
+          DBI::dbWriteTable(
+            glob$pool,
+            "users",
+            users_df_filtered,
+            append = TRUE,
+            row.names = FALSE
           )
         })
       }
@@ -150,7 +183,7 @@ mod_user_manager_server <- function(id, glob) {
       add_permissions_record(
         pool = glob$pool,
         project_id = glob$active_project,
-        permission_user_id = req(input$rql_users), 
+        permission_user_id = req(input$rql_users),
         user_id = glob$user$user_id
       )
       # refresh users for current project
@@ -170,34 +203,40 @@ mod_user_manager_server <- function(id, glob) {
       )
       owner_check <- loc$users_permissions_df %>%
         dplyr::filter(
-          project_id %in% glob$active_project &
+          project_id %in%
+            glob$active_project &
             user_id %in% req(input$members_to_remove)
         ) %>%
         dplyr::pull(project_owner)
-      if (any(owner_check == 1)) warn_user("Project owners cannot be removed from project.")
+      if (any(owner_check == 1)) {
+        warn_user("Project owners cannot be removed from project.")
+      }
       req(all(owner_check == 0))
       remove_permissions_record(
         pool = glob$pool,
         project_id = glob$active_project,
-        permission_user_id = req(input$members_to_remove), 
+        permission_user_id = req(input$members_to_remove),
         user_id = glob$user$user_id
       )
 
       # refresh users for current project
-      loc$project_members_ids <- loc$project_members_ids[loc$project_members_ids != as.integer(input$members_to_remove)]
+      loc$project_members_ids <- loc$project_members_ids[
+        loc$project_members_ids != as.integer(input$members_to_remove)
+      ]
 
       loc$users_permissions_df <- get_user_permissions(
         glob$pool,
         glob$active_project
       )
-      
-      glob$users_observer <- glob$users_observer + 1
 
+      glob$users_observer <- glob$users_observer + 1
     })
 
     # update user selection inputs =======================================================
     observeEvent(c(loc$users_permissions_df, glob$active_project), {
-      loc$users_to_add <- loc$all_users_choices[!loc$all_users_choices %in% as.integer(loc$users_permissions_df$user_id)]
+      loc$users_to_add <- loc$all_users_choices[
+        !loc$all_users_choices %in% as.integer(loc$users_permissions_df$user_id)
+      ]
       if (length(loc$users_to_add) < 1) {
         loc$users_to_add <- c("All registered users have been assigned." = 0)
       }
@@ -225,11 +264,8 @@ mod_user_manager_server <- function(id, glob) {
         choices = stats::setNames(
           loc$users_permissions_df$user_id,
           loc$users_permissions_df$user_name
-          )
+        )
       )
-      
-
-      
     })
 
     # Add user UI =======================================================
@@ -237,53 +273,57 @@ mod_user_manager_server <- function(id, glob) {
       id = "add_user_ui",
       custom_title = "Add users to project",
       custom_tagList = tagList(
-            rql_picker_UI(ns("rql_users"),
-                label = "Select users",
-                none = "Users to add"),
-            rql_button_UI(ns("assign"), 
-            label = "Add users")
-            ),
+        rql_picker_UI(
+          ns("rql_users"),
+          label = "Select users",
+          none = "Users to add"
+        ),
+        rql_button_UI(ns("assign"), label = "Add users")
+      ),
       glob,
       permission = "permissions_modify"
     )
 
-
     # Remove user UI =======================================================
     mod_rql_button_server(
       id = "remove_user_ui",
       custom_title = "Remove users from project",
       custom_tagList = tagList(
-   rql_picker_UI(ns("members_to_remove"), "Select users:", none = "Users to remove"),
-   rql_button_UI(ns("remove_members"), "Remove users")
-            ),
+        rql_picker_UI(
+          ns("members_to_remove"),
+          "Select users:",
+          none = "Users to remove"
+        ),
+        rql_button_UI(ns("remove_members"), "Remove users")
+      ),
       glob,
       permission = "permissions_modify"
     )
 
-   
-   # Modify permissions UI =======================================================
-       mod_rql_button_server(
+    # Modify permissions UI =======================================================
+    mod_rql_button_server(
       id = "modify_permissions_ui",
       custom_title = "Modify user permissions for project",
       custom_tagList = tagList(
-   rql_picker_UI(
-      ns("members_permissions"), 
-      "Select users:",
-      none = "Users to change permissions"),
-    checkboxGroupInput(
-      ns("permissions_list"),
-      label = NULL,
-      choices = stats::setNames(
-          permission(),
-          translate_permissions(permission())
+        rql_picker_UI(
+          ns("members_permissions"),
+          "Select users:",
+          none = "Users to change permissions"
+        ),
+        checkboxGroupInput(
+          ns("permissions_list"),
+          label = NULL,
+          choices = stats::setNames(
+            permission(),
+            translate_permissions(permission())
           )
-    ),
-    rql_button_UI(ns("save_permissions"), "Save permissions")
-            ),
+        ),
+        rql_button_UI(ns("save_permissions"), "Save permissions")
+      ),
       glob,
       permission = "permissions_modify"
     )
-  
+
     # hide save permission UI from users without sufficient permission ======
     observeEvent(loc$users_permissions_df, {
       loc$permissions_modify <- loc$users_permissions_df %>%
@@ -307,6 +347,7 @@ mod_user_manager_server <- function(id, glob) {
           shinyjs::enable("remove_members")
           shinyjs::enable("save_permissions")
         }
-      })
+      }
+    )
   })
-}
\ No newline at end of file
+}