exercise model extension and exercise_type test fix

src/main/kotlin/com/aitrainer/api/model/ExerciseType.kt

@@ -14,9 +14,9 @@ data class ExerciseType (
         @get: NotBlank var name: String = "",        
         @get: NotBlank var description: String = "",
         @get: Null var video: BinaryType?,
-        @get: NotBlank var unit: String = "",
-        @get: Null var unitQuantity: String = "",
-        @get: Null var unitQuantityUnit: String = "",
+        @get: Null var unit: String?,
+        @get: Null var unitQuantity: String?,
+        @get: Null var unitQuantityUnit: String?,
 
 
         @Id @GeneratedValue(strategy = GenerationType.IDENTITY)

src/main/kotlin/com/aitrainer/api/model/Exercises.kt

@@ -15,6 +15,7 @@ data class Exercises (
         @get: NonNull var quantity: Int = 0,
         @get: Null var restTime: Int?, // in seconds
         @get: NonNull var unit: String? = null,
+        @get: NonNull var unitQuantity: Double? = null,
 
         @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
     val exerciseId: Long = 0