Changed initialize to reset.

src/main/kotlin/net/thauvin/erik/readingtime/ReadingTime.kt

@@ -81,19 +81,19 @@ class ReadingTime @JvmOverloads constructor(
 
     var text: String = text
         set(value) {
-            initialize()
+            reset(value != text)
             field = value
         }
 
     var wpm: Int = wpm
         set(value) {
-            initialize()
+            reset(value != wpm)
             field = value
         }
 
     var excludeImages: Boolean = excludeImages
         set(value) {
-            initialize()
+            reset(value != excludeImages)
             field = value
         }
 
@@ -138,7 +138,7 @@ class ReadingTime @JvmOverloads constructor(
         return time
     }
 
-    private fun initialize() {
+    private fun reset(isChanged: Boolean) {
-        readTime = INVALID
+        if (isChanged) readTime = INVALID
     }
 }

src/test/kotlin/net/thauvin/erik/readingtime/ReadingTimeTest.kt

@@ -98,5 +98,9 @@ class ReadingTimeTest {
         rt.text = "This is a test."
         rt.postfix = ""
         assertEquals("1", rt.calcReadingTime())
+
+        rt.text = ""
+        assertEquals("0", rt.calcReadingTime())
+        assertEquals( 0.0, rt.calcReadingTimeInSec())
     }
 }