diff --git a/src/main/java/seedu/address/logic/commands/AddCommand.java b/src/main/java/seedu/address/logic/commands/AddCommand.java
index f42c65314bb..700c1eae231 100644
--- a/src/main/java/seedu/address/logic/commands/AddCommand.java
+++ b/src/main/java/seedu/address/logic/commands/AddCommand.java
@@ -81,6 +81,7 @@ public String execute(Model model) throws CommandException {
      * @throws IllegalArgumentException if the user input does not conform the expected format
      */
     public static AddCommand of(String args) throws IllegalArgumentException {
+        requireNonNull(args);
         ArgumentMultimap argMultimap =
                 ArgumentTokenizer.tokenize(args, PREFIX_NAME, PREFIX_PHONE, PREFIX_EMAIL,
                         PREFIX_ADDRESS, PREFIX_TAG, PREFIX_ASSET);
diff --git a/src/main/java/seedu/address/logic/commands/AssetCommand.java b/src/main/java/seedu/address/logic/commands/AssetCommand.java
index 93b93bbd9cd..7f69ce22fa3 100644
--- a/src/main/java/seedu/address/logic/commands/AssetCommand.java
+++ b/src/main/java/seedu/address/logic/commands/AssetCommand.java
@@ -11,7 +11,7 @@
 import seedu.address.logic.util.ArgumentMultimap;
 import seedu.address.logic.util.ArgumentTokenizer;
 import seedu.address.model.Model;
-import seedu.address.model.asset.Asset;
+import seedu.address.model.person.fields.Asset;
 import seedu.address.model.person.fields.Prefix;
 
 /**
diff --git a/src/main/java/seedu/address/logic/commands/EditCommand.java b/src/main/java/seedu/address/logic/commands/EditCommand.java
index fc007324e6d..5266464173b 100644
--- a/src/main/java/seedu/address/logic/commands/EditCommand.java
+++ b/src/main/java/seedu/address/logic/commands/EditCommand.java
@@ -1,6 +1,7 @@
 package seedu.address.logic.commands;
 
 import static java.util.Objects.requireNonNull;
+import static seedu.address.commons.util.CollectionUtil.requireAllNonNull;
 import static seedu.address.logic.Messages.MESSAGE_INVALID_COMMAND_FORMAT;
 import static seedu.address.model.Model.PREDICATE_SHOW_ALL_PERSONS;
 import static seedu.address.model.person.fields.Address.PREFIX_ADDRESS;
@@ -99,7 +100,7 @@ public String execute(Model model) throws CommandException {
      * edited with {@code editPersonDescriptor}.
      */
     private static Person createEditedPerson(Person personToEdit, EditPersonDescriptor editPersonDescriptor) {
-        assert personToEdit != null;
+        requireAllNonNull(personToEdit, editPersonDescriptor);
 
         Name updatedName = editPersonDescriptor.getName().orElse(personToEdit.getName());
         Phone updatedPhone = editPersonDescriptor.getPhone().orElse(personToEdit.getPhone());
diff --git a/src/main/java/seedu/address/logic/commands/RedoCommand.java b/src/main/java/seedu/address/logic/commands/RedoCommand.java
index e7b2b9a1a64..65cb75e8342 100644
--- a/src/main/java/seedu/address/logic/commands/RedoCommand.java
+++ b/src/main/java/seedu/address/logic/commands/RedoCommand.java
@@ -1,5 +1,7 @@
 package seedu.address.logic.commands;
 
+import static java.util.Objects.requireNonNull;
+
 import seedu.address.logic.commands.exceptions.CommandException;
 import seedu.address.model.Model;
 
@@ -19,6 +21,7 @@ public class RedoCommand extends Command {
 
     @Override
     public String execute(Model model) throws CommandException {
+        requireNonNull(model);
         if (!model.canRedo()) {
             throw new CommandException(MESSAGE_REDO_EXCEPTION);
         }
diff --git a/src/main/java/seedu/address/logic/commands/UndoCommand.java b/src/main/java/seedu/address/logic/commands/UndoCommand.java
index 401b201910b..c1c54d53bd9 100644
--- a/src/main/java/seedu/address/logic/commands/UndoCommand.java
+++ b/src/main/java/seedu/address/logic/commands/UndoCommand.java
@@ -1,5 +1,7 @@
 package seedu.address.logic.commands;
 
+import static java.util.Objects.requireNonNull;
+
 import seedu.address.logic.commands.exceptions.CommandException;
 import seedu.address.model.Model;
 
@@ -18,6 +20,7 @@ public class UndoCommand extends Command {
 
     @Override
     public String execute(Model model) throws CommandException {
+        requireNonNull(model);
         if (!model.canUndo()) {
             throw new CommandException(MESSAGE_UNDO_EXCEPTION);
         }
diff --git a/src/main/java/seedu/address/logic/util/AddressBookParser.java b/src/main/java/seedu/address/logic/util/AddressBookParser.java
index 42664a7efb1..78994ede081 100644
--- a/src/main/java/seedu/address/logic/util/AddressBookParser.java
+++ b/src/main/java/seedu/address/logic/util/AddressBookParser.java
@@ -49,7 +49,7 @@ public static Command parseCommand(String userInput) throws ParseException {
         try {
             commandType = CommandType.valueOf(commandWord.toUpperCase());
         } catch (IllegalArgumentException ie) {
-            logger.finer("This user input caused a ParseException: " + userInput);
+            logger.finer("This user command caused a ParseException: " + userInput);
             throw new ParseException(MESSAGE_UNKNOWN_COMMAND);
         }
 
@@ -57,7 +57,7 @@ public static Command parseCommand(String userInput) throws ParseException {
         try {
             command = commandType.createCommand(arguments);
         } catch (IllegalArgumentException ie) {
-            logger.finer("This user input caused a ParseException: " + userInput);
+            logger.finer("These user command arguments caused a ParseException: " + userInput);
             throw new ParseException(ie.getMessage());
         }
 
diff --git a/src/main/java/seedu/address/model/AddressBook.java b/src/main/java/seedu/address/model/AddressBook.java
index aa29b37fd87..8790b22bd91 100644
--- a/src/main/java/seedu/address/model/AddressBook.java
+++ b/src/main/java/seedu/address/model/AddressBook.java
@@ -9,10 +9,10 @@
 
 import javafx.collections.ObservableList;
 import seedu.address.commons.util.ToStringBuilder;
-import seedu.address.model.asset.Asset;
 import seedu.address.model.exceptions.AddressBookException;
 import seedu.address.model.person.Person;
 import seedu.address.model.person.UniquePersonList;
+import seedu.address.model.person.fields.Asset;
 
 /**
  * Wraps all data at the address-book level.
diff --git a/src/main/java/seedu/address/model/Model.java b/src/main/java/seedu/address/model/Model.java
index 5fd8be05fb3..970a20561f1 100644
--- a/src/main/java/seedu/address/model/Model.java
+++ b/src/main/java/seedu/address/model/Model.java
@@ -5,9 +5,9 @@
 
 import javafx.collections.ObservableList;
 import seedu.address.commons.core.GuiSettings;
-import seedu.address.model.asset.Asset;
 import seedu.address.model.exceptions.AddressBookException;
 import seedu.address.model.person.Person;
+import seedu.address.model.person.fields.Asset;
 
 /**
  * The API of the Model component.
diff --git a/src/main/java/seedu/address/model/ModelManager.java b/src/main/java/seedu/address/model/ModelManager.java
index b1eeff731c5..601f553312d 100644
--- a/src/main/java/seedu/address/model/ModelManager.java
+++ b/src/main/java/seedu/address/model/ModelManager.java
@@ -11,8 +11,8 @@
 import javafx.collections.transformation.FilteredList;
 import seedu.address.commons.core.GuiSettings;
 import seedu.address.commons.core.LogsCenter;
-import seedu.address.model.asset.Asset;
 import seedu.address.model.person.Person;
+import seedu.address.model.person.fields.Asset;
 
 /**
  * Represents the in-memory model of the address book data.
diff --git a/src/main/java/seedu/address/model/person/Person.java b/src/main/java/seedu/address/model/person/Person.java
index 3e8810ab03c..79fd536431a 100644
--- a/src/main/java/seedu/address/model/person/Person.java
+++ b/src/main/java/seedu/address/model/person/Person.java
@@ -8,8 +8,8 @@
 import com.fasterxml.jackson.annotation.JsonProperty;
 
 import seedu.address.commons.util.ToStringBuilder;
-import seedu.address.model.asset.Asset;
 import seedu.address.model.person.fields.Address;
+import seedu.address.model.person.fields.Asset;
 import seedu.address.model.person.fields.Assets;
 import seedu.address.model.person.fields.Email;
 import seedu.address.model.person.fields.Name;
diff --git a/src/main/java/seedu/address/model/asset/Asset.java b/src/main/java/seedu/address/model/person/fields/Asset.java
similarity index 97%
rename from src/main/java/seedu/address/model/asset/Asset.java
rename to src/main/java/seedu/address/model/person/fields/Asset.java
index 5bf6661e6c8..26789d90b6f 100644
--- a/src/main/java/seedu/address/model/asset/Asset.java
+++ b/src/main/java/seedu/address/model/person/fields/Asset.java
@@ -1,4 +1,4 @@
-package seedu.address.model.asset;
+package seedu.address.model.person.fields;
 
 import static java.util.Objects.requireNonNull;
 import static seedu.address.commons.util.AppUtil.checkArgument;
diff --git a/src/main/java/seedu/address/model/person/fields/Assets.java b/src/main/java/seedu/address/model/person/fields/Assets.java
index fca29ae46b2..a75229c7351 100644
--- a/src/main/java/seedu/address/model/person/fields/Assets.java
+++ b/src/main/java/seedu/address/model/person/fields/Assets.java
@@ -10,8 +10,6 @@
 
 import com.fasterxml.jackson.annotation.JsonValue;
 
-import seedu.address.model.asset.Asset;
-
 /**
  * Represents a collection of assets associated to a person in the address book.
  */
diff --git a/src/main/java/seedu/address/model/tag/Tag.java b/src/main/java/seedu/address/model/person/fields/Tag.java
similarity index 97%
rename from src/main/java/seedu/address/model/tag/Tag.java
rename to src/main/java/seedu/address/model/person/fields/Tag.java
index 60c1d5f832d..f557aaa4fe9 100644
--- a/src/main/java/seedu/address/model/tag/Tag.java
+++ b/src/main/java/seedu/address/model/person/fields/Tag.java
@@ -1,4 +1,4 @@
-package seedu.address.model.tag;
+package seedu.address.model.person.fields;
 
 import static java.util.Objects.requireNonNull;
 import static seedu.address.commons.util.AppUtil.checkArgument;
diff --git a/src/main/java/seedu/address/model/person/fields/Tags.java b/src/main/java/seedu/address/model/person/fields/Tags.java
index 005e457b2e8..657f7bde829 100644
--- a/src/main/java/seedu/address/model/person/fields/Tags.java
+++ b/src/main/java/seedu/address/model/person/fields/Tags.java
@@ -9,8 +9,6 @@
 
 import com.fasterxml.jackson.annotation.JsonValue;
 
-import seedu.address.model.tag.Tag;
-
 //@@author aureliony
 /**
  * Represents an abstraction for a list of tags.
diff --git a/src/main/java/seedu/address/ui/PersonCard.java b/src/main/java/seedu/address/ui/PersonCard.java
index 624301ab83c..bb0aadb5da6 100644
--- a/src/main/java/seedu/address/ui/PersonCard.java
+++ b/src/main/java/seedu/address/ui/PersonCard.java
@@ -7,9 +7,9 @@
 import javafx.scene.layout.FlowPane;
 import javafx.scene.layout.HBox;
 import javafx.scene.layout.Region;
-import seedu.address.model.asset.Asset;
 import seedu.address.model.person.Person;
-import seedu.address.model.tag.Tag;
+import seedu.address.model.person.fields.Asset;
+import seedu.address.model.person.fields.Tag;
 
 /**
  * An UI component that displays information of a {@code Person}.
diff --git a/src/test/java/seedu/address/logic/commands/AddCommandTest.java b/src/test/java/seedu/address/logic/commands/AddCommandTest.java
index 0ce120f8232..a75c0808268 100644
--- a/src/test/java/seedu/address/logic/commands/AddCommandTest.java
+++ b/src/test/java/seedu/address/logic/commands/AddCommandTest.java
@@ -59,8 +59,8 @@
 import seedu.address.model.Model;
 import seedu.address.model.ReadOnlyAddressBook;
 import seedu.address.model.ReadOnlyUserPrefs;
-import seedu.address.model.asset.Asset;
 import seedu.address.model.person.Person;
+import seedu.address.model.person.fields.Asset;
 import seedu.address.testutil.PersonBuilder;
 
 public class AddCommandTest {
diff --git a/src/test/java/seedu/address/logic/commands/AssetCommandTest.java b/src/test/java/seedu/address/logic/commands/AssetCommandTest.java
index 0bdc4433513..d3886b6eab6 100644
--- a/src/test/java/seedu/address/logic/commands/AssetCommandTest.java
+++ b/src/test/java/seedu/address/logic/commands/AssetCommandTest.java
@@ -10,7 +10,7 @@
 import static seedu.address.logic.commands.AssetCommand.MESSAGE_NOT_EDITED;
 import static seedu.address.logic.commands.AssetCommand.MESSAGE_SUCCESS;
 import static seedu.address.logic.commands.CommandTestUtil.assertParseFailure;
-import static seedu.address.model.asset.Asset.MESSAGE_CONSTRAINTS;
+import static seedu.address.model.person.fields.Asset.MESSAGE_CONSTRAINTS;
 import static seedu.address.testutil.Assert.assertThrows;
 import static seedu.address.testutil.TypicalPersons.getTypicalAddressBook;
 
@@ -20,8 +20,8 @@
 import seedu.address.model.Model;
 import seedu.address.model.ModelManager;
 import seedu.address.model.UserPrefs;
-import seedu.address.model.asset.Asset;
 import seedu.address.model.person.Person;
+import seedu.address.model.person.fields.Asset;
 import seedu.address.testutil.AssetBuilder;
 import seedu.address.testutil.PersonBuilder;
 
diff --git a/src/test/java/seedu/address/model/asset/AssetTest.java b/src/test/java/seedu/address/model/person/fields/AssetTest.java
similarity index 97%
rename from src/test/java/seedu/address/model/asset/AssetTest.java
rename to src/test/java/seedu/address/model/person/fields/AssetTest.java
index b0064e156fb..05680fce36e 100644
--- a/src/test/java/seedu/address/model/asset/AssetTest.java
+++ b/src/test/java/seedu/address/model/person/fields/AssetTest.java
@@ -1,4 +1,4 @@
-package seedu.address.model.asset;
+package seedu.address.model.person.fields;
 
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
diff --git a/src/test/java/seedu/address/model/person/fields/AssetsTest.java b/src/test/java/seedu/address/model/person/fields/AssetsTest.java
index 34b0eb17673..5aa25eb97b9 100644
--- a/src/test/java/seedu/address/model/person/fields/AssetsTest.java
+++ b/src/test/java/seedu/address/model/person/fields/AssetsTest.java
@@ -10,8 +10,6 @@
 
 import org.junit.jupiter.api.Test;
 
-import seedu.address.model.asset.Asset;
-
 class AssetsTest {
 
     private static final String INVALID_ASSET = " ";
diff --git a/src/test/java/seedu/address/model/tag/TagTest.java b/src/test/java/seedu/address/model/person/fields/TagTest.java
similarity index 97%
rename from src/test/java/seedu/address/model/tag/TagTest.java
rename to src/test/java/seedu/address/model/person/fields/TagTest.java
index 07656b0fc9e..8fed3afbac1 100644
--- a/src/test/java/seedu/address/model/tag/TagTest.java
+++ b/src/test/java/seedu/address/model/person/fields/TagTest.java
@@ -1,4 +1,4 @@
-package seedu.address.model.tag;
+package seedu.address.model.person.fields;
 
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static org.junit.jupiter.api.Assertions.assertEquals;
diff --git a/src/test/java/seedu/address/model/person/fields/TagsTest.java b/src/test/java/seedu/address/model/person/fields/TagsTest.java
index f5625e0af3a..d663825a9c8 100644
--- a/src/test/java/seedu/address/model/person/fields/TagsTest.java
+++ b/src/test/java/seedu/address/model/person/fields/TagsTest.java
@@ -10,8 +10,6 @@
 
 import org.junit.jupiter.api.Test;
 
-import seedu.address.model.tag.Tag;
-
 class TagsTest {
 
     private static final String INVALID_TAG = "#friend";
diff --git a/src/test/java/seedu/address/testutil/AssetBuilder.java b/src/test/java/seedu/address/testutil/AssetBuilder.java
index db0358b8839..3fff8d4af7b 100644
--- a/src/test/java/seedu/address/testutil/AssetBuilder.java
+++ b/src/test/java/seedu/address/testutil/AssetBuilder.java
@@ -1,6 +1,6 @@
 package seedu.address.testutil;
 
-import seedu.address.model.asset.Asset;
+import seedu.address.model.person.fields.Asset;
 
 /**
  * A utility class to help with building Person objects.