feat: add function is blank() to check if a string is blank

src/main/scala/org/camunda/feel/impl/builtin/BooleanBuiltinFunctions.scala

@@ -25,7 +25,8 @@ object BooleanBuiltinFunctions {
     "not"         -> List(notFunction),
     "is defined"  -> List(isDefinedFunction),
     "get or else" -> List(getOrElse),
-    "assert"      -> List(assertFunction, assertFunction2)
+    "assert"      -> List(assertFunction, assertFunction2),
+    "is blank"  -> List(isBlankFunction)
   )
 
   private def notFunction =
@@ -70,4 +71,11 @@ object BooleanBuiltinFunctions {
     }
   )
 
+  private def isBlankFunction = builtinFunction(
+    params = List("string"),
+    invoke = {case List(ValString(string)) =>
+      ValBoolean(string.isBlank)
+    }
+  )
+
 }

src/test/scala/org/camunda/feel/impl/builtin/BuiltinFunctionsTest.scala

@@ -243,4 +243,27 @@ class BuiltinFunctionsTest
       "Assertion failure on evaluate the expression 'list contains(assert(my_list, my_list != null, \"The condition is not true\"), 2)': The condition is not true"
     )
   }
+
+  "A is blank() function" should "return Boolean" in {
+    evaluateExpression(
+      expression = """ is blank("") """
+    ) should returnResult(true)
+
+    evaluateExpression(
+      expression = """ is blank(" ") """
+    ) should returnResult(true)
+
+    evaluateExpression(
+      expression = """ is blank("hello world") """
+    ) should returnResult(false)
+
+    evaluateExpression(
+      expression = """ is blank(" hello world ") """
+    ) should returnResult(false)
+
+    evaluateExpression(
+      expression = """ is blank("\t\n\r\f") """
+    ) should returnResult(true)
+  }
+
 }