diff --git a/src/commands/cmdhandler.py b/src/commands/cmdhandler.py
index fe703d051f..b26a3dc739 100644
--- a/src/commands/cmdhandler.py
+++ b/src/commands/cmdhandler.py
@@ -316,7 +316,6 @@ def cmdhandler(called_by, raw_string, testing=False, callertype="session", sessi
                 else:
                     # fallback to default error text
                     sysarg = _("Command '%s' is not available.") % raw_string
-                    cmdset.get_all_cmd_keys_and_aliases(caller)
                     suggestions = string_suggestions(raw_string, cmdset.get_all_cmd_keys_and_aliases(caller), cutoff=0.7, maxnum=3)
                     if suggestions:
                         sysarg += _(" Maybe you meant %s?") % utils.list_to_string(suggestions, _('or'), addquote=True)
diff --git a/src/commands/command.py b/src/commands/command.py
index 280788515d..3e2fd19a14 100644
--- a/src/commands/command.py
+++ b/src/commands/command.py
@@ -30,7 +30,7 @@ def _init_command(mcs, **kwargs):
             mcs.aliases = [str(alias).strip().lower() for alias in mcs.aliases.split(',')]
         except Exception:
             mcs.aliases = []
-    mcs.aliases = list(set(alias for alias in mcs.aliases if alias != mcs.key))
+    mcs.aliases = list(set(alias for alias in mcs.aliases if alias and alias != mcs.key))
 
     # optimization - a set is much faster to match against than a list
     mcs._matchset = set([mcs.key] + mcs.aliases)
diff --git a/src/typeclasses/models.py b/src/typeclasses/models.py
index 67c704567a..ea9c879ba8 100644
--- a/src/typeclasses/models.py
+++ b/src/typeclasses/models.py
@@ -592,7 +592,7 @@ class TagHandler(object):
 
     def all(self):
         "Get all tags in this handler"
-        return [to_str(p[0]) for p in _GA(self.obj, self._m2m_fieldname).all().values_list("db_key")]
+        return [to_str(p[0]) for p in _GA(self.obj, self._m2m_fieldname).all().values_list("db_key") if p[0]]
 
     def __str__(self):
         return ",".join(self.all())
diff --git a/src/utils/utils.py b/src/utils/utils.py
index 3ef27553de..57cd1ca2fc 100644
--- a/src/utils/utils.py
+++ b/src/utils/utils.py
@@ -39,7 +39,6 @@ def is_iter(iterable):
     except AttributeError:
         return False
 
-
 def make_iter(obj):
     "Makes sure that the object is always iterable."
     return not hasattr(obj, '__iter__') and [obj] or obj
@@ -796,7 +795,7 @@ def string_similarity(string1, string2):
     This implements a "cosine-similarity" algorithm as described for example in
        Proceedings of the 22nd International Conference on Computation Linguistics
        (Coling 2008), pages 593-600, Manchester, August 2008
-    The measure vectors used is simply a "bag of words" type histogram (but for letters).
+    The measure-vectors used is simply a "bag of words" type histogram (but for letters).
 
     The function returns a value 0...1 rating how similar the two strings are. The strings can
     contain multiple words.
@@ -804,8 +803,12 @@ def string_similarity(string1, string2):
     vocabulary = set(list(string1 + string2))
     vec1 = [string1.count(v) for v in vocabulary]
     vec2 = [string2.count(v) for v in vocabulary]
-    return float(sum(vec1[i]*vec2[i] for i in range(len(vocabulary)))) / \
-           (math.sqrt(sum(v1**2 for v1 in vec1)) * math.sqrt(sum(v2**2 for v2 in vec2)))
+    try:
+        return float(sum(vec1[i]*vec2[i] for i in range(len(vocabulary)))) / \
+               (math.sqrt(sum(v1**2 for v1 in vec1)) * math.sqrt(sum(v2**2 for v2 in vec2)))
+    except ZeroDivisionError:
+        # can happen if empty-string cmdnames appear for some reason. This is a no-match.
+        return 0
 
 def string_suggestions(string, vocabulary, cutoff=0.6, maxnum=3):
     """