Allow unitless numerical habits

uhabits-android/src/androidTest/java/org/isoron/uhabits/activities/habits/list/views/NumberButtonViewTest.kt

@@ -73,6 +73,13 @@ class NumberButtonViewTest : BaseViewTest() {
         assertRenders(view, "$PATH/render_above.png")
     }
 
+    @Test
+    fun testRender_emptyUnits() {
+        view.value = 500.0
+        view.units = ""
+        assertRenders(view, "$PATH/render_unitless.png")
+    }
+
     @Test
     fun testRender_belowThreshold() {
         view.value = 99.0

uhabits-android/src/main/java/org/isoron/uhabits/activities/habits/edit/EditHabitActivity.kt

@@ -275,10 +275,6 @@ class EditHabitActivity : AppCompatActivity() {
             isValid = false
         }
         if (habitType == Habit.NUMBER_HABIT) {
-            if (unitInput.text.isEmpty()) {
-                unitInput.error = getFormattedValidationError(R.string.validation_cannot_be_blank)
-                isValid = false
-            }
             if (targetInput.text.isEmpty()) {
                 targetInput.error = getString(R.string.validation_cannot_be_blank)
                 isValid = false

uhabits-android/src/main/java/org/isoron/uhabits/activities/habits/list/views/NumberButtonView.kt

@@ -186,11 +186,16 @@ class NumberButtonView(
             pNumber.typeface = typeface
             pUnit.color = activeColor
 
+            if (units.isBlank()) {
+                rect.set(0f, 0f, width.toFloat(), height.toFloat())
+                rect.offset(0f, 0.5f * em)
+                canvas.drawText(label, rect.centerX(), rect.centerY(), pNumber)
+            } else {
                 rect.set(0f, 0f, width.toFloat(), height.toFloat())
                 canvas.drawText(label, rect.centerX(), rect.centerY(), pNumber)
-
                 rect.offset(0f, 1.3f * em)
                 canvas.drawText(units, rect.centerX(), rect.centerY(), pUnit)
             }
         }
     }
+}