diff --git a/Dockerfile b/Dockerfile
index 101f7a99..665a7e44 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -15,7 +15,7 @@ FROM node:14-buster as builder
 # Install all node dependencies.
 WORKDIR /grist
 COPY package.json yarn.lock /grist/
-RUN yarn install --frozen-lockfile --verbose
+RUN yarn install --frozen-lockfile --verbose --network-timeout 600000
 
 # Install any extra node dependencies (at root level, to avoid having to wrestle
 # with merging them).
@@ -23,7 +23,7 @@ COPY --from=ext / /grist/ext
 RUN \
  mkdir /node_modules && \
  cd /grist/ext && \
- { if [ -e package.json ] ; then yarn install --frozen-lockfile --modules-folder=/node_modules --verbose ; fi }
+ { if [ -e package.json ] ; then yarn install --frozen-lockfile --modules-folder=/node_modules --verbose --network-timeout 600000 ; fi }
 
 # Build node code.
 COPY tsconfig.json /grist
diff --git a/sandbox/grist/imports/fixtures/test_falsy_cells.xlsx b/sandbox/grist/imports/fixtures/test_falsy_cells.xlsx
new file mode 100644
index 00000000..d4efdf50
Binary files /dev/null and b/sandbox/grist/imports/fixtures/test_falsy_cells.xlsx differ
diff --git a/sandbox/grist/imports/import_xls_test.py b/sandbox/grist/imports/import_xls_test.py
index a905ef9a..935c7104 100644
--- a/sandbox/grist/imports/import_xls_test.py
+++ b/sandbox/grist/imports/import_xls_test.py
@@ -189,5 +189,22 @@ class TestImportXLS(unittest.TestCase):
       ],
     }])
 
+  def test_falsy_cells(self):
+    # Falsy cells should be parsed as Numeric, not Date.
+    parsed_file = import_xls.parse_file(*_get_fixture('test_falsy_cells.xlsx'))
+    tables = parsed_file[1]
+    self.assertEqual(tables, [{
+      'table_name': 'Sheet1',
+      'column_metadata': [
+        {'id': u'A', 'type': 'Numeric'},
+        {'id': u'B', 'type': 'Numeric'},
+      ],
+      'table_data': [
+        [0, 0],
+        [0, 0],
+      ],
+    }])
+
+
 if __name__ == '__main__':
   unittest.main()
diff --git a/sandbox/grist/parse_data.py b/sandbox/grist/parse_data.py
index 47f95d04..20ed9ea2 100644
--- a/sandbox/grist/parse_data.py
+++ b/sandbox/grist/parse_data.py
@@ -83,7 +83,7 @@ class SimpleDateTimeConverter(BaseConverter):
   def convert(cls, value):
     if type(value) is datetime.datetime:
       return value
-    elif not value:
+    elif value is None:
       return None
     raise ValueError()
 
diff --git a/test/common/parseDate.ts b/test/common/parseDate.ts
index ec44977e..ad5c8fde 100644
--- a/test/common/parseDate.ts
+++ b/test/common/parseDate.ts
@@ -331,6 +331,7 @@ describe('parseDate', function() {
   });
 
   it('should handle datetimes as formatted by moment', function() {
+    this.timeout(10000);  // there may be a LOT of timezone names.
     for (const date of ['2020-02-03', '2020-06-07', '2020-10-11']) {  // different months for daylight savings
       const dateTime = date + ' 12:34:56';
       const utcMoment = moment.tz(dateTime, 'UTC');