ContextAnalysis: Make naught comparable to struct again.

src/main/java/de/hsrm/compiler/Klang/types/NamedType.java

@@ -21,7 +21,7 @@ public class NamedType extends Type {
 
     @Override
     public Type combine(Type that) {
-        if(this.equals(that)) {
+        if(this.equals(that) || (that instanceof NullType)) {
             return this;
         }
 

src/test/java/NaughtTest.java

@@ -0,0 +1,72 @@
+import de.hsrm.compiler.Klang.ContextAnalysis;
+import org.antlr.v4.runtime.tree.ParseTree;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class NaughtTest {
+    @Test
+    void shouldBeComparableToStruct() {
+        ParseTree tree = Helper.prepareParser("""
+                    struct bar { a: int; }
+                    
+                    function foo(): int {
+                        let a: bar = create bar(1);
+                        if (a == naught) {
+                            return -1;
+                        }
+                        return 1;
+                    }
+                    
+                    foo();
+                """);
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldBeAssignableToStruct() {
+        ParseTree tree = Helper.prepareParser("""
+                    struct bar { a: int; }
+                    
+                    function foo(): int {
+                        let a: bar = naught;
+                        return 1;
+                    }
+                    
+                    foo();
+                """);
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+
+    @Test
+    void shouldBeReturnable() {
+        ParseTree tree = Helper.prepareParser("""
+                    struct bar { a: int; }
+                    
+                    function foo(): bar {
+                        return naught;
+                    }
+                    
+                    foo();
+                """);
+        var ctxAnal = new ContextAnalysis(
+                Helper.getFuncs(tree),
+                Helper.getStructs(tree),
+                Helper.getEnums(tree)
+        );
+
+        assertDoesNotThrow(() -> ctxAnal.visit(tree));
+    }
+}