BUG: Fixes index bug in cast.py for issue pandas-dev#18414

Author: khalludi

pandas/core/dtypes/cast.py

@@ -1376,7 +1376,7 @@ def find_common_type(types):
     if len(types) == 0:
         raise ValueError("no types given")
 
-    first = types[0]
+    first = types.iloc[0]
 
     # workaround for find_common_type([np.dtype('datetime64[ns]')] * 2)
     # => object