Fix a bug for got NPE when eco plugin not installed

Author: sandtechnology

src/main/java/org/maxgamer/quickshop/QuickShop.java

@@ -229,6 +229,7 @@ public class QuickShop extends JavaPlugin implements QuickShopAPI {
      * The economy we hook into for transactions
      */
     @Getter
+    @Nullable
     private AbstractEconomy economy;
     /**
      * Whether or not to limit players shop amounts

src/main/java/org/maxgamer/quickshop/util/economyformatter/EconomyFormatter.java

@@ -24,6 +24,7 @@
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.maxgamer.quickshop.QuickShop;
+import org.maxgamer.quickshop.api.economy.AbstractEconomy;
 import org.maxgamer.quickshop.api.shop.Shop;
 import org.maxgamer.quickshop.util.MsgUtil;
 import org.maxgamer.quickshop.util.Util;
@@ -99,11 +100,12 @@ public String format(double n, boolean internalFormat, @NotNull World world, @Nu
 
     @NotNull
     public String format(double n, boolean internalFormat, @NotNull World world, @Nullable String currency) {
-        if (internalFormat) {
+        AbstractEconomy economy = QuickShop.getInstance().getEconomy();
+        if (internalFormat || economy == null) {
             return getInternalFormat(n, currency);
         }
         try {
-            String formatted = QuickShop.getInstance().getEconomy().format(n, world, currency);
+            String formatted = economy.format(n, world, currency);
             if (StringUtils.isEmpty(formatted)) {
                 Util.debugLog(
                         "Use alternate-currency-symbol to formatting, Cause economy plugin returned null");