Fix generic data class hashCode for null

Null may come from everywhere, so we always check for it (when the property's
type is not primitive)

compiler/backend/src/org/jetbrains/jet/codegen/ImplementationBodyCodegen.java

@@ -506,14 +506,14 @@ public class ImplementationBodyCodegen extends ClassBodyCodegen {
             genPropertyOnStack(iv, propertyDescriptor, 0);
 
             Label ifNull = null;
-            if (propertyDescriptor.getType().isNullable()) {
+            Type asmType = typeMapper.mapType(propertyDescriptor.getType());
+            if (!isPrimitive(asmType)) {
                 ifNull = new Label();
-
                 iv.dup();
                 iv.ifnull(ifNull);
             }
 
-            genHashCode(mv, iv, typeMapper.mapType(propertyDescriptor.getType()));
+            genHashCode(mv, iv, asmType);
 
             if (ifNull != null) {
                 Label end = new Label();

compiler/testData/codegen/dataClasses/hashcode/genericNull.kt

@@ -0,0 +1,7 @@
+data class A<T>(val t: T)
+
+fun box(): String {
+    val h = A<String?>(null).hashCode()
+    if (h != 0) return "Fail $h"
+    return "OK"
+}

compiler/tests/org/jetbrains/jet/codegen/DataClassCodegenTestGenerated.java

@@ -223,6 +223,11 @@ public class DataClassCodegenTestGenerated extends AbstractDataClassCodegenTest
             blackBoxFileByFullPath("compiler/testData/codegen/dataClasses/hashcode/float.kt");
         }
         
+        @TestMetadata("genericNull.kt")
+        public void testGenericNull() throws Exception {
+            blackBoxFileByFullPath("compiler/testData/codegen/dataClasses/hashcode/genericNull.kt");
+        }
+        
         @TestMetadata("int.kt")
         public void testInt() throws Exception {
             blackBoxFileByFullPath("compiler/testData/codegen/dataClasses/hashcode/int.kt");