Fix missing empty constructors for entity classes

src/main/kotlin/com/wbrawner/budgetserver/budget/Budget.kt

@@ -16,7 +16,9 @@ data class Budget(
         @OneToMany(mappedBy = "budget") val transactions: Set<Transaction> = TreeSet(),
         @OneToMany(mappedBy = "budget") val categories: Set<Category> = TreeSet(),
         @ManyToMany val users: Set<User> = mutableSetOf(),
-        @ManyToOne val owner: User
+        @Column(nullable = false)
+        @ManyToOne
+        val owner: User? = null
 )
 
 data class NewBudgetRequest(val name: String, val description: String?, val userIds: Set<Long>)

src/main/kotlin/com/wbrawner/budgetserver/category/Category.kt

@@ -11,7 +11,9 @@ data class Category(
         val title: String = "",
         val description: String? = null,
         val amount: Long = 0,
-        @ManyToOne val budget: Budget,
+        @Column(nullable = false)
+        @ManyToOne
+        val budget: Budget? = null,
         @OneToMany(mappedBy = "category") val transactions: Set<Transaction> = emptySet(),
         val expense: Boolean? = true
 ) : Comparable<Category> {
@@ -31,7 +33,7 @@ data class CategoryResponse(
             category.title,
             category.description,
             category.amount,
-            category.budget.id!!,
+            category.budget!!.id!!,
             category.expense
     )
 }

src/main/kotlin/com/wbrawner/budgetserver/transaction/Transaction.kt

@@ -15,8 +15,12 @@ data class Transaction(
         val amount: Long = 0,
         @ManyToOne val category: Category? = null,
         val expense: Boolean = true,
-        @ManyToOne val createdBy: User,
-        @ManyToOne val budget: Budget
+        @ManyToOne
+        @Column(nullable = false)
+        val createdBy: User? = null,
+        @ManyToOne
+        @Column(nullable = false)
+        val budget: Budget? = null
 ) : Comparable<Transaction> {
     override fun compareTo(other: Transaction): Int = this.date.compareTo(other.date)
 }
@@ -39,9 +43,9 @@ data class TransactionResponse(
             transaction.date.toString(),
             transaction.amount,
             transaction.expense,
-            transaction.budget.id!!,
+            transaction.budget!!.id!!,
             if (transaction.category != null) transaction.category.id!! else null,
-            transaction.createdBy.id!!
+            transaction.createdBy!!.id!!
     )
 }