fix error and warnings in notebook 07

examples/07_mmr_to_mf6_chf_dfw.ipynb

@@ -312,6 +312,7 @@
     "        inflow_dir=inflow_dir,\n",
     "    )\n",
     "\n",
+    "    dfw.write()\n",
     "    success, buff = dfw.run(silent=False, report=True)\n",
     "    assert success"
    ]
@@ -354,7 +355,9 @@
     "n_substeps = int(ndays_run * 24 * 60 * 60 / tdis_perlen * tdis_nstp)\n",
     "substep_len = np.timedelta64(int(tdis_perlen / tdis_nstp), \"s\")\n",
     "sim_end_time = sim_start_time + n_substeps * substep_len\n",
-    "sim_times = np.arange(sim_start_time, sim_end_time, substep_len)\n",
+    "sim_times = np.arange(sim_start_time, sim_end_time, substep_len).astype(\n",
+    "    \"datetime64[ns]\"\n",
+    ")  # ns to avoid xarray warnings\n",
     "perioddata = tdis.perioddata.get_data()\n",
     "assert len(sim_times) == len(perioddata) * perioddata[0][1]"
    ]
@@ -567,10 +570,11 @@
    "outputs": [],
    "source": [
     "# Subset to points of interest (poi), known flow gages\n",
-    "poi_id = np.chararray(\n",
-    "    prms_mf6_ds[\"prms streamflow\"].nhm_seg.shape, unicode=True, itemsize=15\n",
-    ")\n",
     "empty_str = \" \" * 15\n",
+    "poi_id = np.full(\n",
+    "    prms_mf6_ds[\"prms streamflow\"].nhm_seg.shape, empty_str, dtype=\"<U15\"\n",
+    ")\n",
+    "\n",
     "poi_id[:] = empty_str\n",
     "for ii, jj in enumerate(params.parameters[\"poi_gage_segment\"].tolist()):\n",
     "    poi_id[jj] = params.parameters[\"poi_gage_id\"][ii]\n",