Test on null value and new function isNull

Author: PetrPytelka

src/main/java/com/scriptbasic/utility/functions/UtilityFunctions.java

@@ -85,6 +85,15 @@ static public Boolean isDefined(final Object s) {
         return s != null;
     }
 
+    /**
+     * @param s is some value or object
+     * @return true if the parameter is null
+     */
+    @BasicFunction(classification = Utility.class)
+    static public Boolean isNull(final Object s) {
+        return s == null;
+    }
+
     /**
      * Create a new byte buffer of length {@code len}.
      *

src/test/resources/com/scriptbasic/testprograms/TestStringFunctions.bas

@@ -9,6 +9,9 @@ assert("ltrim", ltrim(v)="1234 ")
 assert("trim", trim(v)="1234")
 assert("rtrim", rtrim(v)=" 1234")
 
+' Test null values
+assert("trim_with_null", IsNull(trim(xxx)))
+
 ' Test left, mid, right functions
 v = 1234
 assert("left_with_num", left(v,2)="12")