[python][RDF] Handle the creation of an empty RDataFrame in _MakeNumpyDataFrame

Author: siliataider

bindings/pyroot/pythonizations/python/ROOT/_pythonization/_rdataframe.py

@@ -481,15 +481,21 @@ def pythonize_rdataframe(klass):
 
 
 def _make_name_rvec_pair(key, value):
+    import numpy as np
+
     import ROOT
 
     # Get name of key
     if not isinstance(key, str):
         raise RuntimeError("Object not convertible: Dictionary key is not convertible to a string.")
 
+    if not np.any(value):
+        # If the array is empty, we convert the type from object to short to create a default empty RVec
+        value = value.astype(np.int16)
+
     # Convert value to RVec and attach to dictionary
     pyvec = ROOT.VecOps.AsRVec(value)
-    if not pyvec:
+    if not pyvec and np.any(value):
         raise RuntimeError("Object not convertible: Dictionary entry " + key + " is not convertible with AsRVec.")
 
     # Add pairs of column name and associated RVec to signature