diff --git a/android/assets/jsons/translations/German.properties b/android/assets/jsons/translations/German.properties
index 210cc39ca4..f38b9a5eec 100644
--- a/android/assets/jsons/translations/German.properties
+++ b/android/assets/jsons/translations/German.properties
@@ -366,6 +366,12 @@ Upload map = Karte hochladen
 Could not upload map! = Kann Karte nicht hochladen!
 Map uploaded successfully! = Karte hochladen war erfolgreich!
 Saving... = Speichern...
+It looks like your saved game can't be loaded! = Dieser Spielstand kann nicht geladen werden!
+If you could copy your game data ("Copy saved game to clipboard" -  = Wenn Sie die Spieldaten kopieren ("Gespeichertes Spiel in die Zwischenablage kopieren"),
+  paste into an email to yairm210@hotmail.com) =   und in eine mail an mich (yairm210@hotmail.com) einfügen,
+I could maybe help you figure out what went wrong, since this isn't supposed to happen! = dann kann ich eventuell helfen den Grund zu finden - das sollte nicht passieren!
+Missing mods: [mods] = Der Spielstand benötigt das/die mod(s) [mods], diese sind aber nicht verfügbar.
+
 
 # Options
 
diff --git a/android/assets/jsons/translations/template.properties b/android/assets/jsons/translations/template.properties
index b0c698e18f..d112610b9d 100644
--- a/android/assets/jsons/translations/template.properties
+++ b/android/assets/jsons/translations/template.properties
@@ -366,6 +366,11 @@ Upload map =
 Could not upload map! = 
 Map uploaded successfully! = 
 Saving... = 
+It looks like your saved game can't be loaded! = 
+If you could copy your game data ("Copy saved game to clipboard" -  = 
+  paste into an email to yairm210@hotmail.com) = 
+I could maybe help you figure out what went wrong, since this isn't supposed to happen! = 
+Missing mods: [mods] = 
 
 # Options
 
diff --git a/core/src/com/unciv/logic/GameInfo.kt b/core/src/com/unciv/logic/GameInfo.kt
index cd14ddd747..a20a652ca6 100644
--- a/core/src/com/unciv/logic/GameInfo.kt
+++ b/core/src/com/unciv/logic/GameInfo.kt
@@ -17,6 +17,8 @@ import com.unciv.models.ruleset.RulesetCache
 import java.util.*
 import kotlin.collections.ArrayList
 
+class UncivShowableException(missingMods: String) : Exception(missingMods)
+
 class GameInfo {
     @Transient lateinit var difficultyObject: Difficulty // Since this is static game-wide, and was taking a large part of nextTurn
     @Transient lateinit var currentPlayerCiv:CivilizationInfo // this is called thousands of times, no reason to search for it with a find{} every time
@@ -219,6 +221,15 @@ class GameInfo {
     fun setTransients() {
         tileMap.gameInfo = this
         ruleSet = RulesetCache.getComplexRuleset(gameParameters.mods)
+        // any mod the saved game lists that is currently not installed causes null pointer
+        // exceptions in this routine unless it contained no new objects or was very simple.
+        // Player's fault, so better complain early:
+        val missingMods = gameParameters.mods
+                .filterNot { it in ruleSet.mods }
+                .joinToString(limit = 120) { it }
+        if (missingMods.isNotEmpty()) {
+            throw UncivShowableException("Missing mods: [$missingMods]")
+        }
 
         // Renames as of version 3.1.8, because of translation conflicts with the property "Range" and the difficulty "Immortal"
         // Needs to be BEFORE tileMap.setTransients, because the units' setTransients is called from there
@@ -370,3 +381,4 @@ class GameInfo {
     }
 
 }
+
diff --git a/core/src/com/unciv/models/ruleset/Ruleset.kt b/core/src/com/unciv/models/ruleset/Ruleset.kt
index 77e5a19813..8d2740d3ea 100644
--- a/core/src/com/unciv/models/ruleset/Ruleset.kt
+++ b/core/src/com/unciv/models/ruleset/Ruleset.kt
@@ -3,6 +3,7 @@ package com.unciv.models.ruleset
 import com.badlogic.gdx.Gdx
 import com.badlogic.gdx.files.FileHandle
 import com.unciv.JsonParser
+import com.unciv.logic.UncivShowableException
 import com.unciv.models.ruleset.tech.TechColumn
 import com.unciv.models.ruleset.tech.Technology
 import com.unciv.models.ruleset.tile.Terrain
@@ -91,10 +92,11 @@ class Ruleset() {
         if(buildingsFile.exists()) {
             buildings += createHashmap(jsonParser.getFromJson(Array<Building>::class.java, buildingsFile))
             for (building in buildings.values) {
-                if (building.requiredTech == null) continue
-                val column = technologies[building.requiredTech!!]!!.column
-                if (building.cost == 0)
-                    building.cost = if (building.isWonder || building.isNationalWonder) column!!.wonderCost else column!!.buildingCost
+                if (building.cost == 0) {
+                    val column = technologies[building.requiredTech]?.column
+                            ?: throw UncivShowableException("Building (${building.name}) must either have an explicit cost or a required tech in the same mod")
+                    building.cost = if (building.isWonder || building.isNationalWonder) column.wonderCost else column.buildingCost
+                }
             }
         }
 
@@ -149,14 +151,18 @@ object RulesetCache :HashMap<String,Ruleset>(){
         this[""] = Ruleset().apply { load(Gdx.files.internal("jsons")) }
 
         for(modFolder in Gdx.files.local("mods").list()){
+            if (modFolder.name().startsWith('.')) continue
             try{
                 val modRuleset = Ruleset()
                 modRuleset.load(modFolder.child("jsons"))
                 modRuleset.name = modFolder.name()
                 this[modRuleset.name] = modRuleset
+                println ("Mod loaded successfully: " + modRuleset.name)
             }
             catch (ex:Exception){
-                println( "Exception loading " + modFolder.name() + ": " + ex.message )
+                println ("Exception loading mod '${modFolder.name()}':")
+                println ("  ${ex.localizedMessage}")
+                println ("  (Source file ${ex.stackTrace[0].fileName} line ${ex.stackTrace[0].lineNumber})")
             }
         }
     }
diff --git a/core/src/com/unciv/ui/saves/LoadGameScreen.kt b/core/src/com/unciv/ui/saves/LoadGameScreen.kt
index e807f619f3..084f2610b0 100644
--- a/core/src/com/unciv/ui/saves/LoadGameScreen.kt
+++ b/core/src/com/unciv/ui/saves/LoadGameScreen.kt
@@ -10,6 +10,7 @@ import com.badlogic.gdx.scenes.scene2d.ui.TextButton
 import com.badlogic.gdx.scenes.scene2d.utils.ChangeListener
 import com.unciv.UncivGame
 import com.unciv.logic.GameSaver
+import com.unciv.logic.UncivShowableException
 import com.unciv.models.translations.tr
 import com.unciv.ui.pickerscreens.PickerScreen
 import com.unciv.ui.utils.disable
@@ -44,11 +45,17 @@ class LoadGameScreen : PickerScreen() {
             catch (ex:Exception){
                 val cantLoadGamePopup = Popup(this)
                 cantLoadGamePopup.addGoodSizedLabel("It looks like your saved game can't be loaded!").row()
-                cantLoadGamePopup.addGoodSizedLabel("If you could copy your game data (\"Copy saved game to clipboard\" - ").row()
-                cantLoadGamePopup.addGoodSizedLabel("  paste into an email to yairm210@hotmail.com)").row()
-                cantLoadGamePopup.addGoodSizedLabel("I could maybe help you figure out what went wrong, since this isn't supposed to happen!").row()
-                cantLoadGamePopup.open()
-                ex.printStackTrace()
+                if (ex is UncivShowableException && ex.localizedMessage != null) {
+                    // thrown exceptions are our own tests and can be shown to the user
+                    cantLoadGamePopup.addGoodSizedLabel(ex.localizedMessage).row()
+                    cantLoadGamePopup.open()
+                } else {
+                    cantLoadGamePopup.addGoodSizedLabel("If you could copy your game data (\"Copy saved game to clipboard\" - ").row()
+                    cantLoadGamePopup.addGoodSizedLabel("  paste into an email to yairm210@hotmail.com)").row()
+                    cantLoadGamePopup.addGoodSizedLabel("I could maybe help you figure out what went wrong, since this isn't supposed to happen!").row()
+                    cantLoadGamePopup.open()
+                    ex.printStackTrace()
+                }
             }
         }
 
diff --git a/desktop/src/com/unciv/app/desktop/DesktopLauncher.kt b/desktop/src/com/unciv/app/desktop/DesktopLauncher.kt
index 98813f5b28..ec24fc7849 100644
--- a/desktop/src/com/unciv/app/desktop/DesktopLauncher.kt
+++ b/desktop/src/com/unciv/app/desktop/DesktopLauncher.kt
@@ -61,7 +61,8 @@ internal object DesktopLauncher {
         val modDirectory = File("mods")
         if(modDirectory.exists()) {
             for (mod in modDirectory.listFiles()!!){
-                TexturePacker.process(settings, mod.path + "/Images", mod.path, "game")
+                if (!mod.isHidden && File(mod.path + "/Images").exists())
+                    TexturePacker.process(settings, mod.path + "/Images", mod.path, "game")
             }
         }
 
@@ -97,6 +98,6 @@ internal object DesktopLauncher {
         presence.details=currentPlayerCiv.nation.getLeaderDisplayName().tr()
         presence.largeImageKey = "logo" // The actual image is uploaded to the discord app / applications webpage
         presence.largeImageText ="Turn".tr()+" " + currentPlayerCiv.gameInfo.turns
-        DiscordRPC.INSTANCE.Discord_UpdatePresence(presence);
+        DiscordRPC.INSTANCE.Discord_UpdatePresence(presence)
     }
 }