René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"[BUG] Query error: cell missing value {}","articleBody":"**Describe the bug**\r\nThe python api throws the missing value error to my SPARQL query:\r\n```\r\nSELECT ?name ?proteinExpressionScore\r\nWHERE {\r\n  ?a typeOf HumanProteinOccurrence .\r\n  ?a name ?name .\r\n  ?a proteinExpressionScore ?proteinExpressionScore .\r\n}\r\nLIMIT 2\r\n```\r\n\r\n**To Reproduce**\r\nSteps to reproduce the behavior:\r\n1. Go to a Colab notebook\r\n2. run\r\n```python\r\n!pip install --upgrade --quiet datacommons\r\n# Import Data Commons\r\nimport datacommons as dc\r\nroot = 'https://api.datacommons.org'\r\n\r\nSELECT ?name ?proteinExpressionScore\r\nWHERE {\r\n  ?a typeOf HumanProteinOccurrence .\r\n  ?a name ?name .\r\n  ?a proteinExpressionScore ?proteinExpressionScore .\r\n}\r\nLIMIT 2\r\n```\r\n3. See error\r\n\r\n**Expected behavior**\r\n```python\r\nresult = [{'?name': '2ABD_HUMAN_Pancreas_ExocrineGlandularCells', '?proteinExpressionScore': 'ProteinExpressionLow'},\r\n {'?name': '2A5G_HUMAN_Bronchus_RespiratoryEpithelialCells', '?proteinExpressionScore': 'ProteinExpressionMedium'}]\r\n```\r\n\r\n**Screenshots**\r\nMissing value error: https://screenshot.googleplex.com/fa799d8a-84fb-4972-a73d-c680861d19af\r\nResponse error: https://screenshot.googleplex.com/54176345-fe07-4c5d-91aa-01536ab01141\r\n**Additional context**\r\nResponse error occurs sometimes for the same query as well, as shown in the second screenshoot. \r\n","author":{"url":"https://github.com/mengzhensun","@type":"Person","name":"mengzhensun"},"datePublished":"2020-08-13T18:54:48.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/139/api-python/issues/139"}