diff --git a/common-ktx/src/main/java/co/nimblehq/common/extensions/StringExt.kt b/common-ktx/src/main/java/co/nimblehq/common/extensions/StringExt.kt
index df8332d..d1d4728 100644
--- a/common-ktx/src/main/java/co/nimblehq/common/extensions/StringExt.kt
+++ b/common-ktx/src/main/java/co/nimblehq/common/extensions/StringExt.kt
@@ -2,6 +2,10 @@ package co.nimblehq.common.extensions
 
 import androidx.core.util.PatternsCompat
 import java.util.*
+import kotlin.contracts.ExperimentalContracts
+import kotlin.contracts.contract
+
+private val THAI_REGEX = "([\\u0E00-\\u0E7F]+)".toRegex()
 
 /**
  * Check if the string not null or empty.
@@ -9,7 +13,13 @@ import java.util.*
  *
  * @return true if this nullable char sequence is NOT either null or empty
  */
-fun String?.isNotNullOrEmpty(): Boolean = !this.isNullOrEmpty()
+@OptIn(ExperimentalContracts::class)
+fun String?.isNotNullOrEmpty(): Boolean {
+    contract {
+        returns(true) implies (this@isNotNullOrEmpty != null)
+    }
+    return !this.isNullOrEmpty()
+}
 
 /**
  * Check if the string not null or blank.
@@ -18,7 +28,13 @@ fun String?.isNotNullOrEmpty(): Boolean = !this.isNullOrEmpty()
  * @return true if this nullable char sequence is NOT either null or empty or consists solely of
  * whitespace
  */
-fun String?.isNotNullOrBlank(): Boolean = !this.isNullOrBlank()
+@OptIn(ExperimentalContracts::class)
+fun String?.isNotNullOrBlank(): Boolean {
+    contract {
+        returns(true) implies (this@isNotNullOrBlank != null)
+    }
+    return !this.isNullOrBlank()
+}
 
 /**
  * Eliminate the given character then titleize.
@@ -68,6 +84,5 @@ fun String.isEmailValid(): Boolean {
  * @return true if this string is Thai
  */
 fun String.isThai(): Boolean {
-    val thaiRegex = "([\\u0E00-\\u0E7F]+)".toRegex()
-    return if (isEmpty() || isBlank()) false else all { thaiRegex.matches(it.toString()) }
+    return isNotEmpty() && all { THAI_REGEX.matches(it.toString()) }
 }