None shall not pass args_in_kwargs (GenericMappingTools#1815)

Fixes bug in `args_in_kwargs` function whereby `None` values
are allowed, when actually, we want to drop the `None`.

* Add failing test for when param=0
* Check that argument is not None or False

pygmt/helpers/utils.py

@@ -306,5 +306,23 @@ def args_in_kwargs(args, kwargs):
     --------
     bool
         If one of the required arguments is in ``kwargs``.
+
+    Examples
+    --------
+
+    >>> args_in_kwargs(args=["A", "B"], kwargs={"C": "xyz"})
+    False
+    >>> args_in_kwargs(args=["A", "B"], kwargs={"B": "af"})
+    True
+    >>> args_in_kwargs(args=["A", "B"], kwargs={"B": None})
+    False
+    >>> args_in_kwargs(args=["A", "B"], kwargs={"B": True})
+    True
+    >>> args_in_kwargs(args=["A", "B"], kwargs={"B": False})
+    False
+    >>> args_in_kwargs(args=["A", "B"], kwargs={"B": 0})
+    True
     """
-    return any(arg in kwargs for arg in args)
+    return any(
+        kwargs.get(arg) is not None and kwargs.get(arg) is not False for arg in args
+    )