Don't convert 0 to null on optional output (#1122)

* Don't convert 0 to null on output

* Add test for optional numeric output returning 0.

* Keep conversion to null for optional outputs where glob returns [].

* Add windows_needs_docker to test_optional_numeric_output_0

Author: bogdang989

cwltool/command_line_tool.py

@@ -797,7 +797,12 @@ def collect_output(self,
             adjustFileObjs(r, revmap)
 
             if not r and optional:
-                return None
+                # Don't convert zero or empty string to None
+                if r in [0, '']:
+                    return r
+                # For [] or None, return None
+                else:
+                    return None
 
         if (not empty_and_optional and isinstance(schema["type"], MutableMapping)
                 and schema["type"]["type"] == "record"):

tests/test_examples.py

@@ -920,3 +920,14 @@ def test_v1_0_position_expression():
         ['--debug', get_data(test_file), get_data(test_job)])
     assert "is not int" in stderr, stderr
     assert error_code == 1
+
+
+@windows_needs_docker
+def test_optional_numeric_output_0():
+    test_file = "tests/wf/optional-numerical-output-0.cwl"
+    error_code, stdout, stderr = get_main_output(
+        [get_data(test_file)])
+
+    assert "completed success" in stderr
+    assert error_code == 0
+    assert json.loads(stdout)['out'] == 0

tests/wf/optional-numerical-output-0.cwl

@@ -0,0 +1,16 @@
+cwlVersion: v1.0
+class: CommandLineTool
+baseCommand:
+  - echo
+  - "0"
+stdout: a.txt
+requirements:
+- class: InlineJavascriptRequirement
+inputs: []
+outputs:
+  out:
+    type: float?
+    outputBinding:
+      glob: "a.txt"
+      loadContents: true
+      outputEval: "${\n    return parseFloat(self[0].contents);\n}"