has() should only test for the presence of the argument

and not consider its value. treat arguments with a set default value as
present.

modules/core/include/opencv2/core/utility.hpp

@@ -607,6 +607,10 @@ For example:
 }
 @endcode
 
+Note that there are no default values for `help` and `timestamp` so we can check their presence using the `has()` method.
+Arguments with default values are considered to be always present. Use the `get()` method in these cases to check their
+actual value instead.
+
 ### Usage
 
 For the described keys:

modules/core/src/command_line_parser.cpp

@@ -334,9 +334,9 @@ bool CommandLineParser::has(const String& name) const
     {
         for (size_t j = 0; j < impl->data[i].keys.size(); j++)
         {
-            if (name.compare(impl->data[i].keys[j]) == 0 && String("true").compare(impl->data[i].def_value) == 0)
+            if (name == impl->data[i].keys[j])
             {
-                return true;
+                return !impl->cat_string(impl->data[i].def_value).empty();
             }
         }
     }