src/de/steamwar/command/AbstractSWCommand.java

@@ -76,7 +76,8 @@ public abstract class AbstractSWCommand<T> {
                     errors.forEach(Runnable::run);
                     return;
                 }
-                commandHelpList.stream().anyMatch(s -> s.invoke((ignore) -> {}, sender, alias, args));
+                commandHelpList.stream().anyMatch(s -> s.invoke((ignore) -> {
+                }, sender, alias, args));
             }
         } catch (CommandNoHelpException e) {
             // Ignored
@@ -361,4 +362,9 @@ public abstract class AbstractSWCommand<T> {
          */
         boolean allowEAs() default true;
     }
+
+    @Retention(RetentionPolicy.RUNTIME)
+    @Target({ElementType.PARAMETER})
+    protected @interface AllowNull {
+    }
 }

src/de/steamwar/command/CommandPart.java

@@ -52,6 +52,9 @@ class CommandPart<T> {
     @Setter
     private boolean onlyUseIfNoneIsGiven = false;
 
+    @Setter
+    private boolean allowNullValues = false;
+
     public CommandPart(AbstractSWCommand<T> command, AbstractTypeMapper<T, ?> typeMapper, AbstractValidator<T, Object> validator, Class<?> varArgType, String optional) {
         this.command = command;
         this.typeMapper = typeMapper;
@@ -183,7 +186,7 @@ class CommandPart<T> {
                     return new CheckArgumentResult(false, null);
                 }
             }
-            return new CheckArgumentResult(value != null, value);
+            return new CheckArgumentResult(allowNullValues || value != null, value);
         } catch (Exception e) {
             return new CheckArgumentResult(false, null);
         }

src/de/steamwar/command/SWCommandUtils.java

@@ -94,9 +94,11 @@ public class SWCommandUtils {
             AbstractValidator<T, Object> validator = (AbstractValidator<T, Object>) getValidator(parameter, localValidator);
             Class<?> varArgType = parameter.isVarArgs() ? parameter.getType().getComponentType() : null;
             AbstractSWCommand.OptionalValue optionalValue = parameter.getAnnotation(AbstractSWCommand.OptionalValue.class);
+            AbstractSWCommand.AllowNull allowNull = parameter.getAnnotation(AbstractSWCommand.AllowNull.class);
 
             CommandPart<T> commandPart = new CommandPart<>(command, typeMapper, validator, varArgType, optionalValue != null ? optionalValue.value() : null);
             commandPart.setOnlyUseIfNoneIsGiven(optionalValue != null && optionalValue.onlyUINIG());
+            commandPart.setAllowNullValues(allowNull != null);
             if (current != null) {
                 current.setNext(commandPart);
             }

testsrc/de/steamwar/command/NullMapperCommand.java

@@ -0,0 +1,59 @@
+/*
+ * This file is a part of the SteamWar software.
+ *
+ * Copyright (C) 2022  SteamWar.de-Serverteam
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package de.steamwar.command;
+
+import de.steamwar.command.dto.ExecutionIdentifier;
+import de.steamwar.command.dto.TestSWCommand;
+import de.steamwar.command.dto.TestTypeMapper;
+
+import java.util.Collection;
+
+public class NullMapperCommand extends TestSWCommand {
+
+    public NullMapperCommand() {
+        super("nullmapper");
+    }
+
+    @Register
+    public void test(String sender, @AllowNull String arg) {
+        if (arg == null) {
+            throw new ExecutionIdentifier("null");
+        }
+        throw new ExecutionIdentifier("notnull");
+    }
+
+    @ClassMapper(value = String.class, local = true)
+    public TestTypeMapper<String> typeMapper() {
+        return new TestTypeMapper<String>() {
+            @Override
+            public String map(String sender, String[] previousArguments, String s) {
+                if (s.equals("Hello World")) {
+                    return null;
+                }
+                return s;
+            }
+
+            @Override
+            public Collection<String> tabCompletes(String sender, String[] previousArguments, String s) {
+                return null;
+            }
+        };
+    }
+}

testsrc/de/steamwar/command/NullMapperCommandTest.java

@@ -0,0 +1,52 @@
+/*
+ * This file is a part of the SteamWar software.
+ *
+ * Copyright (C) 2022  SteamWar.de-Serverteam
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package de.steamwar.command;
+
+import de.steamwar.command.dto.ExecutionIdentifier;
+import org.junit.Test;
+
+import static de.steamwar.AssertionUtils.assertCMDFramework;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.is;
+
+public class NullMapperCommandTest {
+
+    @Test
+    public void testNull() {
+        NullMapperCommand command = new NullMapperCommand();
+        try {
+            command.execute("test", "", new String[] {"Hello World"});
+            assertThat(true, is(false));
+        } catch (Exception e) {
+            assertCMDFramework(e, ExecutionIdentifier.class, "null");
+        }
+    }
+
+    @Test
+    public void testNonNull() {
+        NullMapperCommand command = new NullMapperCommand();
+        try {
+            command.execute("test", "", new String[] {"Hello"});
+            assertThat(true, is(false));
+        } catch (Exception e) {
+            assertCMDFramework(e, ExecutionIdentifier.class, "notnull");
+        }
+    }
+}