diff --git a/src/models/User.ts b/src/models/User.ts
index c17ca9d..8bc9ef0 100644
--- a/src/models/User.ts
+++ b/src/models/User.ts
@@ -1,143 +1,150 @@
-import mongoose, { Document, Schema } from 'mongoose';
-
-import ImageService from '../services/ImageService';
-import AuthUtils from '../utils/AuthUtils';
-import { Model } from '../utils/constants';
-import { AuthTokens, BaseModel } from '../utils/types';
-
-/**
- * (2.01) TODO:
- * - Read this interface.
- * - Delete this comment once you've done so.
- */
-interface IUser extends BaseModel {
-  email?: string;
-
-  /**
-   * First name of the user. This is optional b/c when we first create a user,
-   * this is not required.
-   */
-  firstName?: string;
-
-  /**
-   * URL of the user's Instagram profile, if any.
-   */
-  instagramUrl?: string;
-
-  /**
-   * Last name of the user. This is optional b/c when we first create a user,
-   * this is not required.
-   */
-  lastName?: string;
-
-  /**
-   * URL of the user's LinkedIn profile, if any.
-   */
-  linkedInUrl?: string;
-
-  phoneNumber: string;
-
-  /**
-   * Key of the object in the Digital Ocean Spaces bucket that hosts the
-   * user's profile picture.
-   */
-  profilePictureKey?: string;
-
-  /**
-   * URL where the user's profile picture is hosted. This will most likely
-   * be a DigitalOcean URL.
-   */
-  profilePictureUrl?: string;
-
-  /**
-   * Unique JWT token that allows a user to refresh their authentication status
-   * in a request flow.
-   */
-  refreshToken?: string;
-
-  /**
-   * URL of the user's Twitter profile, if any.
-   */
-  twitterUrl?: string;
-}
-
-export type UserDocument = Document<{}, {}, IUser> &
-  IUser & {
-    renewToken: () => Promise<AuthTokens>;
-  };
-
-const userSchema: Schema<UserDocument> = new Schema<UserDocument>(
-  {
-    /**
-     * (2.02) TODO:
-     * - Create the schema for the Users that we'll save in the database using
-     * the interface above as a reference.
-     * - Delete this comment and the example field.
-     * - Add comment(s) to explain your work.
-     */
-    exampleField: { required: false, type: String, unique: false },
-
-    // We shouldn't be returning the refreshToken when fetching a user from
-    // the database, since that is sensitive information.
-    refreshToken: { required: false, select: false, type: String }
-  },
-  {
-    timestamps: true,
-    toJSON: { virtuals: true },
-    toObject: { virtuals: true }
-  }
-);
-
-type TokenArgs = {
-  date: number;
-  id: string;
-};
-
-/**
- * (2.03) TODO:
- * - Read the below function and try to explain to yourself what's going on!
- * - Delete this comment.
- */
-/**
- * Creates and returns a new access and refresh token for the user. It also
- * persists the refresh token to the database, so we can associate the token
- * and lookup a user by their refresh token in our authentication flows.
- */
-userSchema.methods.renewToken = async function (): Promise<AuthTokens> {
-  const accessToken: string = AuthUtils.signToken<TokenArgs>(
-    { date: Date.now(), id: this._id },
-    60 * 60 // Expires in 1 hour.
-  );
-
-  const refreshToken: string = AuthUtils.signToken<TokenArgs>(
-    { date: Date.now(), id: this._id },
-    60 * 60 * 24 * 100 // Expires in 100 days.
-  );
-
-  this.refreshToken = refreshToken;
-  await this.save();
-
-  return {
-    accessToken,
-    refreshToken
-  };
-};
-
-/**
- * Returns the full URL to the profile picture of the user, which is
- * constructed by the key which is stored on record.
- *
- * If there is no profile picture key, returns null.
- */
-userSchema.virtual('profilePictureUrl').get(function () {
-  return this.profilePictureKey
-    ? ImageService.getImageUrl(this.profilePictureKey)
-    : null;
-});
-
-const User: mongoose.Model<UserDocument> = mongoose.model<UserDocument>(
-  Model.USER,
-  userSchema
-);
-
-export default User;
+import mongoose, { Document, Schema } from 'mongoose';
+
+import ImageService from '../services/ImageService';
+import AuthUtils from '../utils/AuthUtils';
+import { Model } from '../utils/constants';
+import { AuthTokens, BaseModel } from '../utils/types';
+
+/**
+ * (2.01) TODO:
+ * - Read this interface.
+ * - Delete this comment once you've done so.
+ */
+interface IUser extends BaseModel {
+  email?: string;
+
+  /**
+   * First name of the user. This is optional b/c when we first create a user,
+   * this is not required.
+   */
+  firstName?: string;
+
+  /**
+   * URL of the user's Instagram profile, if any.
+   */
+  instagramUrl?: string;
+
+  /**
+   * Last name of the user. This is optional b/c when we first create a user,
+   * this is not required.
+   */
+  lastName?: string;
+
+  /**
+   * URL of the user's LinkedIn profile, if any.
+   */
+  linkedInUrl?: string;
+
+  phoneNumber: string;
+
+  /**
+   * Key of the object in the Digital Ocean Spaces bucket that hosts the
+   * user's profile picture.
+   */
+  profilePictureKey?: string;
+
+  /**
+   * URL where the user's profile picture is hosted. This will most likely
+   * be a DigitalOcean URL.
+   */
+  profilePictureUrl?: string;
+
+  /**
+   * Unique JWT token that allows a user to refresh their authentication status
+   * in a request flow.
+   */
+  refreshToken?: string;
+
+  /**
+   * URL of the user's Twitter profile, if any.
+   */
+  twitterUrl?: string;
+}
+
+export type UserDocument = Document<{}, {}, IUser> &
+  IUser & {
+    renewToken: () => Promise<AuthTokens>;
+  };
+
+const userSchema: Schema<UserDocument> = new Schema<UserDocument>(
+  {
+    email: { required: false, sparse: true, type: String, unique: true },
+
+    firstName: { required: false, type: String },
+
+    instagramUrl: { required: false, type: String },
+
+    lastName: { required: false, type: String },
+
+    linkedInUrl: { required: false, type: String },
+
+    phoneNumber: { required: true, type: String, unique: true },
+
+    profilePictureKey: { required: false, type: String },
+
+    // We shouldn't be returning the refreshToken when fetching a user from
+    // the database, since that is sensitive information.
+    refreshToken: { required: false, select: false, type: String },
+
+    twitterUrl: { required: false, type: String }
+  },
+  {
+    timestamps: true,
+    toJSON: { virtuals: true },
+    toObject: { virtuals: true }
+  }
+);
+
+type TokenArgs = {
+  date: number;
+  id: string;
+};
+
+/**
+ * (2.03) TODO:
+ * - Read the below function and try to explain to yourself what's going on!
+ * - Delete this comment.
+ */
+/**
+ * Creates and returns a new access and refresh token for the user. It also
+ * persists the refresh token to the database, so we can associate the token
+ * and lookup a user by their refresh token in our authentication flows.
+ */
+userSchema.methods.renewToken = async function (): Promise<AuthTokens> {
+  const accessToken: string = AuthUtils.signToken<TokenArgs>(
+    { date: Date.now(), id: this._id },
+    60 * 60 // Expires in 1 hour.
+  );
+
+  const refreshToken: string = AuthUtils.signToken<TokenArgs>(
+    { date: Date.now(), id: this._id },
+    60 * 60 * 24 * 100 // Expires in 100 days.
+  );
+
+  this.refreshToken = refreshToken;
+  await this.save();
+
+  return {
+    accessToken,
+    refreshToken
+  };
+};
+
+/**
+ * Returns the full URL to the profile picture of the user, which is
+ * constructed by the key which is stored on record.
+ *
+ * If there is no profile picture key, returns null.
+ */
+userSchema.virtual('profilePictureUrl').get(function () {
+  return this.profilePictureKey
+    ? ImageService.getImageUrl(this.profilePictureKey)
+    : null;
+});
+
+const User: mongoose.Model<UserDocument> = mongoose.model<UserDocument>(
+  Model.USER,
+  userSchema
+);
+
+export default User;