prevent parsing empty uri

csvwlib/converter/ToRDFConverter.py

@@ -82,7 +82,7 @@ def parse_virtual_columns(self, row_node, atdm_row, table_metadata):
                     self.graph.add((row_node, CSVW.describes, subject))
             else:
                 print(f"term {virtual_column['propertyUrl']} not in namespaces")
-S
+
     def _add_file_metadata(self, metadata, node):
         language = JSONLDUtils.language(self.metadata.get('@context',[]))
         for key, value in metadata.items():
@@ -165,6 +165,8 @@ def _object_node(value, col_metadata, atdm_row, tm_url):
 
     @staticmethod
     def _normalize_to_uri(string):
+        if string in [None, '']:
+            return ''
         string = quote(string, safe='')
         string = string.replace('-', '%2D')
         return string

csvwlib/utils/TypeConverter.py

@@ -5,7 +5,7 @@ class TypeConverter:
 
     @staticmethod
     def convert_if_necessary(value, column_metadata):
-        if 'datatype' not in column_metadata:
+        if 'datatype' not in column_metadata or not isinstance(column_metadata['datatype'], dict):
             return value
 
         return TypeConverter.convert(value, column_metadata['datatype'])

csvwlib/utils/metadata.py

@@ -101,7 +101,7 @@ def validate_metadata(self, metadata):
             self.check_titles(table)
 
     def check_csv_reference(self, table, metadata):
-        if not self.start_url.endswith('.csv'):
+        if not (self.start_url or "").endswith('.csv'):
             return
         if table['url'] != self.start_url:
             for key in list(metadata.keys()):