diff --git a/Changelog.md b/Changelog.md
index 00575c6..f2e0170 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -1,3 +1,34 @@
+# 3.3.0 (22 May 2021)
+bugfixes, improvements
+
+### Changes
+ - The flakes cmdline api has been changed. New usage:
+   ```
+   nix (build|shell) mach-nix#gen.(python|docker).package1.package2...
+   ```
+   (Despite this change being backward incompatible, I did not bump the major version since everything flakes related should be considered experimental anyways)
+
+### Improvements
+ - Mach-nix (used via flakes) will now throw an error if the selected nixpkgs version is newer than the dependency DB since this can cause conflicts in the resulting environment.
+ - When used via flakes, it was impossible to select the python version because the import function is not used anymore. Now `python` can be passed to `mkPython` alternatively.
+ - For the flakes cmdline api, collisions are now ignored by default
+ - The simplified override interface did not deal well with non-existent values. 
+    - Now the `.add` directive automatically assumes an empty list/set/string when the attribute to be extended doesn't exist.
+    - Now the `.mod` directive will pass `null` to the given function if the attribute to modify doesn't exist instead.
+
+### Fixes
+ - Generating an environment with a package named `overrides` failed due to a variable name collision in the resulting nix expression.
+ - When used via flakes, the pypiData was downloaded twice, because the legacy code path for fetching was still used instead of the flakes input.
+ - `nix flake show mach-nix` failed because it required IFD for foreign platforms.
+ - For environments generated via `mach-nix env ...` the `python` command referred to the wrong interpreter.
+ - When checking wheels for compatibility, the minor version for python was not respected which could lead to invalid environments.
+ - Some python modules in nixpkgs propagate unnecessary dependencies which could lead to collisions in the final environment. Now mach-nix recursively removes all python dependencies which are not strictly required.
+
+### Package Fixes
+ - cryptography: remove rust related hook when version < 3.4
+
+
+
 # 3.2.0 (11 Mar 2021)
 bugfixes, ignoreCollisions
 
diff --git a/default.nix b/default.nix
index 9a94277..ba2dda1 100644
--- a/default.nix
+++ b/default.nix
@@ -110,7 +110,6 @@ rec {
   # expose dot interface for flakes cmdline
   "with" = pythonWith;
   pythonWith = (withDot (__mkPython "'.pythonWith'")).pythonWith;
-  shellWith = (withDot (__mkPython "'.shellWith'")).shellWith;
   dockerImageWith = (withDot (__mkPython "'.dockerImageWith'")).dockerImageWith;
 
   # expose mach-nix' nixpkgs
diff --git a/flake.nix b/flake.nix
index d9ac192..b6e8fb9 100644
--- a/flake.nix
+++ b/flake.nix
@@ -19,7 +19,7 @@
           true
         else
           false;
-      usageGen = "usage: nix (build|develop) mach-nix#gen.(python|shell|docker).package1.package2...";
+      usageGen = "usage: nix (build|shell) mach-nix#gen.(python|docker).package1.package2...";
     in
       (flake-utils.lib.eachDefaultSystem (system:
         let
@@ -49,11 +49,9 @@
               src = throw usageGen;
               passthru = {
                 python = mach-nix-default.pythonWith;
-                shell = mach-nix-default.shellWith;
                 docker = mach-nix-default.dockerImageWith;
                 inherit (mach-nix-default)
                   pythonWith
-                  shellWith
                   dockerImageWith;
               };
             };
diff --git a/interpreter.nix b/interpreter.nix
index ac24b5a..64acaef 100644
--- a/interpreter.nix
+++ b/interpreter.nix
@@ -1,7 +1,7 @@
 # python interpreter for dev environment
 let
   pkgs = import (import ./mach_nix/nix/nixpkgs-src.nix) { config = {}; };
-  python = pkgs.python37;
+  python = pkgs.python38;
   deps = (pkgs.lib.attrValues (import ./mach_nix/nix/python-deps.nix { inherit python; fetchurl = pkgs.fetchurl; }));
 in
 python.withPackages (ps: deps ++ [
diff --git a/mach_nix/data/providers.py b/mach_nix/data/providers.py
index d200e33..094a430 100644
--- a/mach_nix/data/providers.py
+++ b/mach_nix/data/providers.py
@@ -199,10 +199,10 @@ class CombinedDependencyProvider(DependencyProviderBase):
                               f"Consider adding them via 'providers='"
         else:
             error_text += \
-                f"\nIf the package's initial release date predates the release date of mach-nix, " \
-                f"either upgrade mach-nix itself or manually specify 'pypi_deps_db_commit' and\n" \
-                f"'pypi_deps_db_sha256 for a newer commit of https://github.com/DavHau/pypi-deps-db/commits/master\n" \
-                f"If it still doesn't work, there was probably a problem while crawling pypi.\n" \
+                f"\nThe required package might just not yet be part of the dependency DB currently used.\n" \
+                f"The DB can be updated by specifying 'pypiDataRev' when importing mach-nix.\n" \
+                f"For examples see: https://github.com/DavHau/mach-nix/blob/master/examples.md\n" \
+                f"If it still doesn't work, there might have bene an error while building the DB.\n" \
                 f"Please open an issue at: https://github.com/DavHau/mach-nix/issues/new\n"
         print(error_text, file=sys.stderr)
         exit(1)
diff --git a/mach_nix/fixes.nix b/mach_nix/fixes.nix
index 0141271..d613143 100644
--- a/mach_nix/fixes.nix
+++ b/mach_nix/fixes.nix
@@ -20,28 +20,36 @@ let
     result = parse('${ver1}') ${op} parse('${ver2}')
     print(json.dumps(result))
   '';
+
+  # prevent the normal fitler from being used
+  filter = raise "Error: only use filterSafe (doesn't crash on null input)";
+
+  # filter function that doesn't crash on 'objects = null'
+  # This is important because null will be returned whenever the attribute to modify doesn't exist
+  filterSafe = func: objects: if isNull objects then [] else builtins.filter func objects;
+
 in
 
 
 ### Put Fixes here
 rec {
 
-###  FORMAT  ############################################################################
-#                                                                                       #
-#   package-to-fix = {                                                                  #
-#     name-of-the-fix = {                                                               #
-#       # optionally limit the fix to a condtion                                        #
-#       _cond = {prov, ver, ... }: some boolean expression;                             #
-#                                                                                       #
-#       # define overrides                                                              #
-#       key-to-override = ...;                                 # replace                #
-#       key-to-override.add = ...;                             # append                 #
-#       key-to-override.mod = oldVal: ...;                     # modify                 #
-#       key-to-override.mod = pySelf: oldAttrs: oldVal: ...;   # modify (more args)     #
-#     };                                                                                #
-#   };                                                                                  #
-#                                                                                       #
-#########################################################################################
+###  FORMAT  ##################################################################################
+#                                                                                             #
+#   package-to-fix = {                                                                        #
+#     name-of-the-fix = {                                                                     #
+#       # optionally limit the fix to a condtion                                              #
+#       _cond = {prov, ver, ... }: some boolean expression;                                   #
+#                                                                                             #
+#       # define overrides                                                                    #
+#       key-to-override = ...;                                 # replace                      #
+#       key-to-override.add = ...;                             # append (list/attrs/string)   #
+#       key-to-override.mod = oldVal: ...;                     # modify                       #
+#       key-to-override.mod = pySelf: oldAttrs: oldVal: ...;   # modify (accessing all pkgs)  #
+#     };                                                                                      #
+#   };                                                                                        #
+#                                                                                             #
+###############################################################################################
 
 ### _cond ####################################
 #  possible arguments:                       #
@@ -57,7 +65,7 @@ rec {
 
   cryptography.no-rust-build = {
     _cond = { prov, ver, ... }: prov == "sdist" && comp_ver ver "<" "3.4";
-    nativeBuildInputs.mod = old: filter (inp: (inp.name or "") != "cargo-setup-hook.sh") old;
+    nativeBuildInputs.mod = old: filterSafe (inp: (inp.name or "") != "cargo-setup-hook.sh") old;
   };
 
   # remove if merged: https://github.com/NixOS/nixpkgs/pull/114384
@@ -83,7 +91,7 @@ rec {
 
   pip.remove-reproducible-patch = {
     _cond = { prov, ver, ... }: prov == "sdist" && comp_ver ver "<" "20.0";
-    patches.mod = oldPatches: filter (patch: ! hasSuffix "reproducible.patch" patch) oldPatches;
+    patches.mod = oldPatches: filterSafe (patch: ! hasSuffix "reproducible.patch" patch) oldPatches;
   };
 
   pyqt5 = {
@@ -91,7 +99,7 @@ rec {
       # fix mach-nix induced problem: mach-nix removes all previous python inputs from propagatedBuildInputs
       _cond = {prov, ... }: prov == "nixpkgs";
       propagatedBuildInputs.mod = pySelf: oldAttrs: oldVal:
-        (filter (p: p.pname != "pyqt5-sip") oldVal) ++ [ pySelf.sip pySelf.dbus-python ];
+        (filterSafe (p: p.pname != "pyqt5-sip") oldVal) ++ [ pySelf.sip pySelf.dbus-python ];
     };
     fix-wheel-inputs = {
       _cond = {prov, ... }: prov == "wheel";
@@ -106,7 +114,7 @@ rec {
       # https://github.com/rpy2/rpy2/commit/39e1cb6fca0d4107f1078727d8670c422e3c6f7f
       prov == "sdist"
       && comp_ver ver ">=" "3.2.6";
-    patches.mod = oldPatches: filter (p: ! hasSuffix "pandas-1.x.patch" p) oldPatches;
+    patches.mod = oldPatches: filterSafe (p: ! hasSuffix "pandas-1.x.patch" p) oldPatches;
   };
 
   tensorflow.rm-tensorboard = {
diff --git a/mach_nix/flake.lock b/mach_nix/flake.lock
index 8d8d9ec..f9b13cb 100644
--- a/mach_nix/flake.lock
+++ b/mach_nix/flake.lock
@@ -34,11 +34,11 @@
     "pypi-deps-db": {
       "flake": false,
       "locked": {
-        "lastModified": 1620853232,
-        "narHash": "sha256-SeePgys1mlGUrN/YhCRoo8nApRx5H+KKjyKM1zQ+yAE=",
+        "lastModified": 1621672288,
+        "narHash": "sha256-hUOZnSr1ZaTCOUlC8k946RyRjZsfN2w/9jzic0UKj58=",
         "owner": "DavHau",
         "repo": "pypi-deps-db",
-        "rev": "15175225c8295e08e5b95b2965892820a64e9746",
+        "rev": "19dc04a5c7412431a58a07ceecfe7b3ed3c164a5",
         "type": "github"
       },
       "original": {
diff --git a/mach_nix/generate.py b/mach_nix/generate.py
index 1e2a1f5..24d1e3a 100644
--- a/mach_nix/generate.py
+++ b/mach_nix/generate.py
@@ -90,8 +90,12 @@ def handle_resolution_impossible(exc: ResolutionImpossible, reqs_str, providers_
         f"Python: {py_ver_str}\n"
         f"Cause: {exc.__context__}\n"
         f"The requirements which caused the error:"
-        f"{causes_str}\n",
-        file=sys.stderr)
+        f"{causes_str}\n"
+        f"\nThe given requirements might contain package versions which are not yet part of the dependency DB\n"
+        f"currently used. The DB can be updated by specifying 'pypiDataRev' when importing mach-nix.\n"
+        f"For examples see: https://github.com/DavHau/mach-nix/blob/master/examples.md\n",
+        file=sys.stderr
+    )
 
 
 def main():
diff --git a/mach_nix/nix/compileOverrides.nix b/mach_nix/nix/compileOverrides.nix
index c752ba6..f0c33f7 100644
--- a/mach_nix/nix/compileOverrides.nix
+++ b/mach_nix/nix/compileOverrides.nix
@@ -44,8 +44,8 @@ let
   nixpkgs_json = import ./nixpkgs-json.nix {
     inherit overrides pkgs python;
   };
-  builder_python = pkgs.pkgsBuildHost.python37.withPackages(ps:
-    (pkgs.lib.attrValues (import ./python-deps.nix {python = pkgs.python37; fetchurl = pkgs.fetchurl; }))
+  builder_python = pkgs.pkgsBuildHost.python38.withPackages(ps:
+    (pkgs.lib.attrValues (import ./python-deps.nix {python = pkgs.python38; fetchurl = pkgs.fetchurl; }))
   );
 
   src = ./../../.;
diff --git a/mach_nix/nix/deps-db-and-fetcher.nix b/mach_nix/nix/deps-db-and-fetcher.nix
index 8bb668b..ff1b212 100644
--- a/mach_nix/nix/deps-db-and-fetcher.nix
+++ b/mach_nix/nix/deps-db-and-fetcher.nix
@@ -21,18 +21,11 @@ let
     inherit pkgs;
   };
 in
-let
-  pypi_deps_db_src = pkgs.buildEnv {
-    name = "pypi-deps-db-src";
-    paths = [ deps_db_src ];
-  };
-in
-{ inherit
-    pypi_deps_db_src
+{
+  pypi_deps_db_src = deps_db_src;
+  inherit
     pypi_fetcher_src
-
     pypi_fetcher_commit
     pypi_fetcher_sha256
-
     pypi_fetcher;
 }
diff --git a/mach_nix/nix/lib.nix b/mach_nix/nix/lib.nix
index 503ae46..d3c2535 100644
--- a/mach_nix/nix/lib.nix
+++ b/mach_nix/nix/lib.nix
@@ -242,9 +242,9 @@ rec {
   };
 
   combine = pname: key: val1: val2:
-    if isList val2 then val1 ++ val2
-    else if isAttrs val2 then val1 // val2
-    else if isString val2 then val1 + val2
+    if isList val2 then (if ! isNull val1 then val1 else []) ++ val2
+    else if isAttrs val2 then (if ! isNull val1 then val1 else {}) // val2
+    else if isString val2 then (if ! isNull val1 then val1 else "") + val2
     else throw "_.${pname}.${key}.add only accepts list or attrs or string.";
 
   fixes_to_overrides = fixes:
@@ -258,14 +258,14 @@ rec {
               mapAttrs (key: val:
                 trace "\napplying fix '${fix}' (${key}) for ${pkg}:${oa.version}\n" (
                   if isAttrs val && hasAttr "add" val then
-                    combine pkg key oa."${key}" val.add
+                    combine pkg key (oa."${key}" or null) val.add
                   else if isAttrs val && hasAttr "mod" val && isFunction val.mod then
-                    let result = val.mod oa."${key}"; in
+                    let result = val.mod (oa."${key}" or null); in
                       # if the mod function wants more argument, call with more arguments (alternative style)
                       if ! isFunction result then
                         result
                       else
-                          val.mod pySelf oa oa."${key}"
+                          val.mod pySelf oa (oa."${key}" or null)
                   else
                     val
                 )
diff --git a/mach_nix/nix/python.nix b/mach_nix/nix/python.nix
index ba249a5..90aa41f 100644
--- a/mach_nix/nix/python.nix
+++ b/mach_nix/nix/python.nix
@@ -4,7 +4,7 @@
 }:
 with pkgs;
 let
-  python = python37;
+  python = python38;
   python_deps = (lib.attrValues (import ./python-deps.nix { inherit python; fetchurl = fetchurl; }));
 in
 python.withPackages ( ps: python_deps )
diff --git a/mach_nix/nix/withDot.nix b/mach_nix/nix/withDot.nix
index 23d7906..ed56d7b 100644
--- a/mach_nix/nix/withDot.nix
+++ b/mach_nix/nix/withDot.nix
@@ -23,6 +23,5 @@ let
 in
 {
  "pythonWith" = gen "" [];
- "shellWith" = gen "env" [];
  "dockerImageWith" = gen "dockerImage" [];
 }
diff --git a/shell.nix b/shell.nix
index 42a69f9..f572ae4 100644
--- a/shell.nix
+++ b/shell.nix
@@ -4,7 +4,7 @@
 }:
 with pkgs;
 let
-  python = python37;
+  python = python38;
   machnixDeps = (lib.attrValues (import ./mach_nix/nix/python-deps.nix { inherit python; fetchurl = fetchurl; }));
 in
 mkShell {
diff --git a/tests/test_flakes.nix b/tests/test_flakes.nix
index 55f1dab..ca51f06 100644
--- a/tests/test_flakes.nix
+++ b/tests/test_flakes.nix
@@ -5,7 +5,6 @@
 with builtins;
 let
   pyEnv = (builtins.getFlake (toString ../.)).packages.x86_64-linux.gen.python.requests;
-  pyEnvShell = (builtins.getFlake (toString ../.)).packages.x86_64-linux.gen.shell.requests;
   pyEnvDockerImage = (builtins.getFlake (toString ../.)).packages.x86_64-linux.gen.docker.requests;
 in
 (map (p:
@@ -15,7 +14,7 @@ in
     throw "Error"
 ) [pyEnv pyEnvDockerImage])
 ++ [
-  (if ! pyEnvShell ? _passthru.python.pkgs.requests then
+  (if ! pyEnv ? _passthru.python.pkgs.requests then
     throw "Error with shell"
   else
     mach-nix.nixpkgs.hello)