diff --git a/rocrate/cli.py b/rocrate/cli.py
index 7512383..0f02132 100644
--- a/rocrate/cli.py
+++ b/rocrate/cli.py
@@ -39,25 +39,23 @@ class State:
 @click.pass_context
 def cli(ctx, crate_dir):
     ctx.obj = state = State()
-    state.crate_dir = crate_dir
+    state.crate_dir = os.getcwd() if not crate_dir else os.path.abspath(crate_dir)
 
 
 @cli.command()
 @click.option('--gen-preview', is_flag=True)
 @click.pass_obj
 def init(state, gen_preview):
-    crate_dir = state.crate_dir or os.getcwd()
-    crate = ROCrate(crate_dir, init=True, gen_preview=gen_preview)
-    crate.metadata.write(crate_dir)
+    crate = ROCrate(state.crate_dir, init=True, gen_preview=gen_preview)
+    crate.metadata.write(state.crate_dir)
     if crate.preview:
-        crate.preview.write(crate_dir)
+        crate.preview.write(state.crate_dir)
 
 
 @cli.group()
 @click.pass_obj
 def add(state):
-    crate_dir = state.crate_dir or os.getcwd()
-    state.crate = ROCrate(crate_dir, init=False, gen_preview=False)
+    state.crate = ROCrate(state.crate_dir, init=False, gen_preview=False)
 
 
 @add.command()
@@ -65,16 +63,15 @@ def add(state):
 @click.option('-l', '--language', type=click.Choice(LANG_CHOICES), default="cwl")
 @click.pass_obj
 def workflow(state, path, language):
-    crate_dir = state.crate_dir or os.getcwd()
     source = Path(path).resolve(strict=True)
     try:
-        dest_path = source.relative_to(crate_dir)
+        dest_path = source.relative_to(state.crate_dir)
     except ValueError:
         # For now, only support marking an existing file as a workflow
-        raise ValueError(f"{source} is not in the crate dir")
+        raise ValueError(f"{source} is not in the crate dir {state.crate_dir}")
     # TODO: add command options for main and gen_cwl
     state.crate.add_workflow(source, dest_path, main=True, lang=language, gen_cwl=False)
-    state.crate.metadata.write(crate_dir)
+    state.crate.metadata.write(state.crate_dir)
 
 
 @add.command(name="test-suite")
@@ -83,9 +80,8 @@ def workflow(state, path, language):
 @click.option('-m', '--main-entity')
 @click.pass_obj
 def suite(state, identifier, name, main_entity):
-    crate_dir = state.crate_dir or os.getcwd()
     suite_ = state.crate.add_test_suite(identifier=identifier, name=name, main_entity=main_entity)
-    state.crate.metadata.write(crate_dir)
+    state.crate.metadata.write(state.crate_dir)
     print(suite_.id)
 
 
@@ -98,9 +94,8 @@ def suite(state, identifier, name, main_entity):
 @click.option('-n', '--name')
 @click.pass_obj
 def instance(state, suite, url, resource, service, identifier, name):
-    crate_dir = state.crate_dir or os.getcwd()
     instance_ = state.crate.add_test_instance(suite, url, resource=resource, service=service, identifier=identifier, name=name)
-    state.crate.metadata.write(crate_dir)
+    state.crate.metadata.write(state.crate_dir)
     print(instance_.id)
 
 
@@ -111,23 +106,21 @@ def instance(state, suite, url, resource, service, identifier, name):
 @click.option('-v', '--engine-version')
 @click.pass_obj
 def definition(state, suite, path, engine, engine_version):
-    crate_dir = state.crate_dir or os.getcwd()
     source = Path(path).resolve(strict=True)
     try:
-        dest_path = source.relative_to(crate_dir)
+        dest_path = source.relative_to(state.crate_dir)
     except ValueError:
         # For now, only support marking an existing file as a test definition
-        raise ValueError(f"{source} is not in the crate dir")
+        raise ValueError(f"{source} is not in the crate dir {state.crate_dir}")
     state.crate.add_test_definition(suite, source=source, dest_path=dest_path, engine=engine, engine_version=engine_version)
-    state.crate.metadata.write(crate_dir)
+    state.crate.metadata.write(state.crate_dir)
 
 
 @cli.command()
 @click.argument('dst', type=click.Path(writable=True))
 @click.pass_obj
 def write_zip(state, dst):
-    crate_dir = state.crate_dir or os.getcwd()
-    crate = ROCrate(crate_dir, init=True, gen_preview=False)
+    crate = ROCrate(state.crate_dir, init=True, gen_preview=False)
     crate.write_zip(dst)
 
 
diff --git a/rocrate/model/file.py b/rocrate/model/file.py
index 4b5cc50..8005fcf 100644
--- a/rocrate/model/file.py
+++ b/rocrate/model/file.py
@@ -20,10 +20,9 @@
 import os
 from pathlib import Path
 import shutil
-import urllib
+import urllib.request
 
 from io import IOBase
-from shutil import copy
 from urllib.error import HTTPError
 
 from .data_entity import DataEntity
@@ -38,20 +37,14 @@ class File(DataEntity):
             properties = {}
         self.fetch_remote = fetch_remote
         self.source = source
-        is_local = is_remote = False
-        if isinstance(source, (str, Path)):
-            is_local = os.path.isfile(str(source))
-            is_remote = is_url(str(source))
-            if not is_local and not is_remote:
-                raise ValueError(f"'{source}' is not a path to a local file or a valid remote URI")
-        elif dest_path is None:
+        if not isinstance(source, (str, Path)) and dest_path is None:
             raise ValueError("dest_path must be provided if source is not a path or URI")
         if dest_path:
             # the entity is refrencing a path relative to the ro-crate root
             identifier = Path(dest_path).as_posix()  # relative path?
         else:
             # if there is no dest_path there must be a URI/local path as source
-            if is_local:
+            if not is_url(str(source)):
                 # local source -> becomes local reference = reference relative
                 # to ro-crate root
                 identifier = os.path.basename(source)
@@ -105,23 +98,16 @@ class File(DataEntity):
             out_file_path.parent.mkdir(parents=True, exist_ok=True)
             with open(out_file_path, 'w') as out_file:
                 out_file.write(self.source.getvalue())
-        else:
-            if os.path.isfile(self.source):
-                out_file_path.parent.mkdir(parents=True, exist_ok=True)
-                copy(self.source, out_file_path)
-            else:
-                if self.fetch_remote:
-                    # Legacy version
-                    # urllib.request.urlretrieve(self.source, out_file_path)
-                    # can check that the encodingFormat and contentSize matches
-                    # the request data? i.e.:
-                    # response.getheader('Content-Length') == \
-                    #   self._jsonld['contentSize']
-                    # this would help check if the dataset to be retrieved is
-                    # in fact what was registered in the first place.
-                    out_file_path.parent.mkdir(parents=True, exist_ok=True)
-                    with urllib.request.urlopen(self.source) as response, open(out_file_path, 'wb') as out_file:
-                        shutil.copyfileobj(response, out_file)
+        elif is_url(str(self.source)) and self.fetch_remote:
+            # Should we check that the resource hasn't changed? E.g., compare
+            # response.getheader('Content-Length') to self._jsonld['contentSize'] or
+            # response.getheader('Content-Type') to self._jsonld['encodingFormat']
+            out_file_path.parent.mkdir(parents=True, exist_ok=True)
+            with urllib.request.urlopen(self.source) as response, open(out_file_path, 'wb') as out_file:
+                shutil.copyfileobj(response, out_file)
+        elif os.path.isfile(self.source):
+            out_file_path.parent.mkdir(parents=True, exist_ok=True)
+            shutil.copy(self.source, out_file_path)
 
     def write_zip(self, zip_out):
         if self.id not in zip_out.namelist():
diff --git a/rocrate/rocrate.py b/rocrate/rocrate.py
index a968f10..029b8e3 100644
--- a/rocrate/rocrate.py
+++ b/rocrate/rocrate.py
@@ -21,7 +21,6 @@ import importlib
 import json
 import os
 import uuid
-import requests
 import zipfile
 import atexit
 import shutil
@@ -206,25 +205,21 @@ class ROCrate():
             if 'File' in entity_types:
                 # temporary workaround, should be handled in the general case
                 cls = TestDefinition if "TestDefinition" in entity_types else File
-                file_path = os.path.join(source, entity['@id'])
-                identifier = entity.pop('@id', None)
-                if os.path.exists(file_path):
-                    # referencing a file path relative to crate-root
-                    instance = cls(self, file_path, identifier, properties=entity)
+                identifier = entity['@id']
+                props = {k: v for k, v in entity.items() if k != '@id'}
+                if is_url(identifier):
+                    instance = cls(self, source=identifier, properties=props)
                 else:
-                    # check if it is a valid absolute URI
-                    try:
-                        requests.get(identifier)
-                        instance = cls(self, identifier, properties=entity)
-                    except requests.ConnectionError:
-                        print("Source is not a valid URI")
+                    instance = cls(
+                        self,
+                        source=os.path.join(source, identifier),
+                        dest_path=identifier,
+                        properties=props
+                    )
             if 'Dataset' in entity_types:
                 dir_path = os.path.join(source, entity['@id'])
-                if os.path.exists(dir_path):
-                    props = {k: v for k, v in entity.items() if k != '@id'}
-                    instance = Dataset(self, dir_path, entity['@id'], props)
-                else:
-                    raise Exception('Directory not found')
+                props = {k: v for k, v in entity.items() if k != '@id'}
+                instance = Dataset(self, dir_path, entity['@id'], props)
             self.add(instance)
             added_entities.append(data_entity_id)
 

diff --git a/test/test_read.py b/test/test_read.py
index a3e334b..e170040 100644
--- a/test/test_read.py
+++ b/test/test_read.py
@@ -269,3 +269,32 @@ def test_extra_data(test_data_dir, tmpdir, to_zip):
         assert (out_path / rel).is_file()
         with open(crate_dir / rel) as f1, open(out_path / rel) as f2:
             assert f1.read() == f2.read()
+
+
+def test_missing_dir(test_data_dir, tmpdir):
+    crate_dir = test_data_dir / 'read_crate'
+    name = 'examples'
+    shutil.rmtree(crate_dir / name)
+    crate = ROCrate(crate_dir)
+
+    examples_dataset = crate.dereference(name)
+    assert examples_dataset.id == f'{name}/'
+
+    out_path = tmpdir / 'crate_read_out'
+    crate.write_crate(out_path)
+    assert not (out_path / 'README.txt').exists()
+
+
+def test_missing_file(test_data_dir, tmpdir):
+    crate_dir = test_data_dir / 'read_crate'
+    name = 'test_file_galaxy.txt'
+    test_path = crate_dir / name
+    test_path.unlink()
+    crate = ROCrate(crate_dir)
+
+    test_file = crate.dereference(name)
+    assert test_file.id == name
+
+    out_path = tmpdir / 'crate_read_out'
+    crate.write_crate(out_path)
+    assert not (out_path / name).exists()
diff --git a/test/test_write.py b/test/test_write.py
index c83797c..102d793 100644
--- a/test/test_write.py
+++ b/test/test_write.py
@@ -165,14 +165,22 @@ def test_remote_uri_exceptions(tmpdir):
 
 
 @pytest.mark.parametrize("fetch_remote,validate_url", [(False, False), (False, True), (True, False), (True, True)])
-def test_missing_source(test_data_dir, fetch_remote, validate_url):
-    crate = ROCrate()
+def test_missing_source(test_data_dir, tmpdir, fetch_remote, validate_url):
     path = test_data_dir / uuid.uuid4().hex
-    with pytest.raises(ValueError):
-        crate.add_file(str(path), fetch_remote=fetch_remote, validate_url=validate_url)
+    args = {"fetch_remote": fetch_remote, "validate_url": validate_url}
 
-    with pytest.raises(ValueError):
-        crate.add_file(str(path), path.name, fetch_remote=fetch_remote, validate_url=validate_url)
+    crate = ROCrate()
+    file_ = crate.add_file(str(path), **args)
+    assert file_ is crate.dereference(path.name)
+    out_path = tmpdir / 'ro_crate_out_1'
+    crate.write_crate(out_path)
+    assert not (out_path / path.name).exists()
+
+    crate = ROCrate()
+    file_ = crate.add_file(str(path), path.name, **args)
+    assert file_ is crate.dereference(path.name)
+    out_path = tmpdir / 'ro_crate_out_2'
+    assert not (out_path / path.name).exists()
 
 
 @pytest.mark.parametrize("fetch_remote,validate_url", [(False, False), (False, True), (True, False), (True, True)])

Bug? Fails to load a crate file without its data entities  (directories)
I think this is a bug.

On loading a directory with ONLY the sample file from here: https://raw.githubusercontent.com/ResearchObject/example-ro-sample-image-crate/main/sample-crate/ro-crate-metadata.jsonld

```
from rocrate.rocrate import ROCrate

crate = ROCrate("sample") 
```

It dies like this:
```
Traceback (most recent call last):
  File "/Users/pt/working/ro-crate-py/test.py", line 3, in <module>
    crate = ROCrate("sample") 
  File "/Users/pt/rocrate/lib/python3.9/site-packages/rocrate/rocrate.py", line 92, in __init__
    self.build_crate(entities, source_path, gen_preview)
  File "/Users/pt/rocrate/lib/python3.9/site-packages/rocrate/rocrate.py", line 226, in build_crate
    raise Exception('Directory not found')
Exception: Directory not found

```

Expected behaviour:

I would expect to be able to load an incomplete crate if I am:
- Writing an HTML renderer
- Writing a validator and I want to report all the errors (rather than dying on the first one



 
test/test_read.py::test_missing_dir test/test_read.py::test_missing_file test/test_write.py::test_missing_source[False-False] test/test_write.py::test_missing_source[False-True] test/test_write.py::test_missing_source[True-False] test/test_write.py::test_missing_source[True-True]
test/test_read.py::test_crate_dir_loading[False-False] test/test_read.py::test_crate_dir_loading[True-False] test/test_read.py::test_crate_dir_loading[True-True] test/test_read.py::test_legacy_crate test/test_read.py::test_bad_crate test/test_read.py::test_init[False] test/test_read.py::test_init[True] test/test_read.py::test_init_preview[False-False] test/test_read.py::test_init_preview[False-True] test/test_read.py::test_init_preview[True-False] test/test_read.py::test_init_preview[True-True] test/test_read.py::test_no_parts test/test_read.py::test_extra_data[False] test/test_read.py::test_extra_data[True] test/test_write.py::test_file_writing[False-False] test/test_write.py::test_file_writing[False-True] test/test_write.py::test_file_writing[True-False] test/test_write.py::test_file_writing[True-True] test/test_write.py::test_file_stringio test/test_write.py::test_remote_uri[False] test/test_write.py::test_remote_uri[True] test/test_write.py::test_remote_uri_exceptions test/test_write.py::test_stringio_no_dest[False-False] test/test_write.py::test_stringio_no_dest[False-True] test/test_write.py::test_stringio_no_dest[True-False] test/test_write.py::test_stringio_no_dest[True-True] test/test_write.py::test_no_source_no_dest[False-False] test/test_write.py::test_no_source_no_dest[False-True] test/test_write.py::test_no_source_no_dest[True-False] test/test_write.py::test_no_source_no_dest[True-True] test/test_write.py::test_dataset test/test_write.py::test_no_parts test/test_write.py::test_no_zip_in_zip