Ignore empty lines when deserializing ndjson.

"The [Json] parser MAY silently ignore empty lines, e.g. \n\n".
https://github.com/ndjson/ndjson-spec#32-parsing

[Bug]

build.xml

@@ -122,9 +122,9 @@
 
 			<classpath>
 				<pathelement location="${tlc}/tla2tools.jar" />
-                <pathelement location="${lib}/gson-2.8.6.jar" />
-                <pathelement location="${lib}/jgrapht-core-1.5.1.jar" />
-                <pathelement location="${lib}/jungrapht-layout-1.4-SNAPSHOT.jar" />
+				<pathelement location="${lib}/gson-2.8.6.jar" />
+				<pathelement location="${lib}/jgrapht-core-1.5.1.jar" />
+				<pathelement location="${lib}/jungrapht-layout-1.4-SNAPSHOT.jar" />
 				<pathelement location="${lib}/slf4j-api-1.7.30.jar" />
 				<pathelement location="${lib}/slf4j-nop-1.7.30.jar" />
 				<pathelement location="${lib}/commons-lang3-3.12.0.jar" />
@@ -136,7 +136,7 @@
 
 		<!-- Test if trace expressions involving the ShiViz module work correctly. -->
 		<!-- This test expects TLC to report a liveness violation, which is why    -->
-		<!-- failonerror is off.  Instead, the ant records TLC's return value in   -->
+		<!-- failonerror is off.  Instead, ant records TLC's return value in       -->
 		<!-- shiviz.return.value, which is cheked in the conditional below.        -->
 		<java classname="tlc2.TLC" fork="true" failonerror="false" resultproperty="shiviz.return.value">
 			<!-- Tell Java to use a garbage collector which makes TLC happy. -->

modules/tlc2/overrides/Json.java

@@ -110,8 +110,13 @@ public static IValue ndDeserialize(final StringValue path) throws IOException {
     try (BufferedReader reader = new BufferedReader(new FileReader(new File(path.val.toString())))) {
       String line = reader.readLine();
       while (line != null) {
-        JsonElement node = JsonParser.parseString(line);
-        values.add(getValue(node));
+    	// Ignore empty lines in the newline delimited Json file.
+    	// see https://github.com/ndjson/ndjson-spec#32-parsing
+    	line = line.trim();
+    	if (!"".equals(line)) {
+    		JsonElement node = JsonParser.parseString(line);
+    		values.add(getValue(node));
+    	}
         line = reader.readLine();
       }
     }

tests/JsonTests.ndjson

@@ -0,0 +1,7 @@
+
+
+{"a":3}
+    [[1,2],"look"]
+[[{"b":{"c":[4,5,6]}}]]  
+
+

tests/JsonTests.tla

@@ -160,4 +160,10 @@ RoundTrip ==
        /\ JsonSerialize("build/json/test.json", output)
        /\ output = JsonDeserialize("build/json/test.json")
 ASSUME(RoundTrip)
+
+\* Deserialize existing ndjson with trailing white spaces and (empty) newlines.
+
+ASSUME LET input == <<[a |-> 3], <<<<1, 2>>, "look">>, << <<[b |-> [c |-> <<4, 5, 6>>]]>> >> >>
+       IN  input = ndJsonDeserialize("tests/JsonTests.ndjson")
+
 =============================================================================