Merge pull request #927 from skayliu/skayliu-is-blank

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

Author: saig0

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

@@ -45,7 +45,8 @@ object StringBuiltinFunctions {
     "extract"          -> List(extractFunction),
     "trim"             -> List(trimFunction),
     "uuid"             -> List(uuidFunction),
-    "to base64"        -> List(toBase64Function)
+    "to base64"        -> List(toBase64Function),
+    "is blank"         -> List(isBlankFunction)
   )
 
   private def substringFunction = builtinFunction(
@@ -287,4 +288,11 @@ object StringBuiltinFunctions {
       }
     )
 
+  private def isBlankFunction = builtinFunction(
+    params = List("string"),
+    invoke = {case List(ValString(string)) =>
+      ValBoolean(string.isBlank)
+    }
+  )
+
 }

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

@@ -195,4 +195,32 @@ class BuiltinStringFunctionsTest
 
     evaluateExpression(""" to base64(value: "Camunda") """) should returnResult("Q2FtdW5kYQ==")
   }
+
+  "A is blank() function" should "return true if the string contains only whitespace" in {
+    evaluateExpression(
+      expression = """ is blank("") """
+    ) should returnResult(true)
+
+    evaluateExpression(
+      expression = """ is blank(" ") """
+    ) should returnResult(true)
+
+    evaluateExpression(
+      expression = """ is blank("\t\n\r\f") """
+    ) should returnResult(true)
+
+    evaluateExpression(
+      expression = """ is blank(string: "") """
+    ) should returnResult(true)
+  }
+
+  it should "return false if the string contains only non-whitespace characters" in {
+    evaluateExpression(
+      expression = """ is blank("hello world") """
+    ) should returnResult(false)
+
+    evaluateExpression(
+      expression = """ is blank(" hello world ") """
+    ) should returnResult(false)
+  }
 }