diff --git a/plugins/dbms/maxdb/enumeration.py b/plugins/dbms/maxdb/enumeration.py
index 6f8e9fb52..2afb0b350 100644
--- a/plugins/dbms/maxdb/enumeration.py
+++ b/plugins/dbms/maxdb/enumeration.py
@@ -64,7 +64,7 @@ class Enumeration(GenericEnumeration):
         else:
             dbs = self.getDbs()
 
-        for db in dbs:
+        for db in filter(None, dbs):
             dbs[dbs.index(db)] = safeSQLIdentificatorNaming(db)
 
         infoMsg = "fetching tables for database"
diff --git a/plugins/dbms/mssqlserver/enumeration.py b/plugins/dbms/mssqlserver/enumeration.py
index bcc4b342d..016f18198 100644
--- a/plugins/dbms/mssqlserver/enumeration.py
+++ b/plugins/dbms/mssqlserver/enumeration.py
@@ -77,6 +77,8 @@ class Enumeration(GenericEnumeration):
         for db in dbs:
             dbs[dbs.index(db)] = safeSQLIdentificatorNaming(db)
 
+        dbs = filter(None, dbs)
+
         infoMsg = "fetching tables for database"
         infoMsg += "%s: %s" % ("s" if len(dbs) > 1 else "", ", ".join(db for db in sorted(dbs)))
         logger.info(infoMsg)
diff --git a/plugins/dbms/sybase/enumeration.py b/plugins/dbms/sybase/enumeration.py
index 2e4c5f8e1..2c40fae03 100644
--- a/plugins/dbms/sybase/enumeration.py
+++ b/plugins/dbms/sybase/enumeration.py
@@ -120,6 +120,8 @@ class Enumeration(GenericEnumeration):
         for db in dbs:
             dbs[dbs.index(db)] = safeSQLIdentificatorNaming(db)
 
+        dbs = filter(None, dbs)
+
         infoMsg = "fetching tables for database"
         infoMsg += "%s: %s" % ("s" if len(dbs) > 1 else "", ", ".join(db for db in sorted(dbs)))
         logger.info(infoMsg)
diff --git a/plugins/generic/enumeration.py b/plugins/generic/enumeration.py
index 59ce9797d..d21ac3379 100644
--- a/plugins/generic/enumeration.py
+++ b/plugins/generic/enumeration.py
@@ -252,6 +252,8 @@ class Enumeration:
         else:
             users = []
 
+        users = filter(None, users)
+
         if isTechniqueAvailable(PAYLOAD.TECHNIQUE.UNION) or isTechniqueAvailable(PAYLOAD.TECHNIQUE.ERROR) or conf.direct:
             if Backend.isDbms(DBMS.MSSQL) and Backend.isVersionWithin(("2005", "2008")):
                 query = rootQuery.inband.query2
@@ -447,6 +449,8 @@ class Enumeration:
         else:
             users = []
 
+        users = filter(None, users)
+
         # Set containing the list of DBMS administrators
         areAdmins = set()
 
@@ -830,6 +834,8 @@ class Enumeration:
         for db in dbs:
             dbs[dbs.index(db)] = safeSQLIdentificatorNaming(db)
 
+        dbs = filter(None, dbs)
+
         if bruteForce:
             resumeAvailable = False
 
@@ -998,6 +1004,8 @@ class Enumeration:
         for col in colList:
             colList[colList.index(col)] = safeSQLIdentificatorNaming(col)
 
+        colList = filter(None, colList)
+
         if conf.tbl:
             if Backend.getIdentifiedDbms() in (DBMS.ORACLE, DBMS.DB2):
                 conf.tbl = conf.tbl.upper()
@@ -1388,7 +1396,7 @@ class Enumeration:
             lengths[column] = 0
             entries[column] = BigArray()
 
-        colList = sorted(colList, key=lambda x: len(x) if x else MAX_INT)
+        colList = filter(None, sorted(colList, key=lambda x: len(x) if x else MAX_INT))
 
         for column in colList:
             infoMsg = "fetching number of distinct "
@@ -1550,7 +1558,7 @@ class Enumeration:
 
                     continue
 
-                colList = kb.data.cachedColumns[safeSQLIdentificatorNaming(conf.db)][safeSQLIdentificatorNaming(tbl, True)].keys()
+                colList = filter(None, kb.data.cachedColumns[safeSQLIdentificatorNaming(conf.db)][safeSQLIdentificatorNaming(tbl, True)].keys())
                 colString = ", ".join(column for column in sorted(colList))
                 rootQuery = queries[Backend.getIdentifiedDbms()].dump_table
 
@@ -1856,7 +1864,7 @@ class Enumeration:
                     continue
 
                 conf.tbl = table
-                conf.col = ",".join(column for column in sorted(columns))
+                conf.col = ",".join(column for column in filter(None, sorted(columns)))
                 kb.data.cachedColumns = {}
                 kb.data.dumpedTable = {}