Fix NPE in dateDiff exception message & fix bullet list formatting in semantics doc CTR

Author: xiazcy

docs/src/dev/provider/gremlin-semantics.asciidoc

@@ -610,6 +610,7 @@ None
 Incoming date remains unchanged.
 
 *Exceptions*
+
 * If the incoming traverser is a non-String/Number/Date value then an `IllegalArgumentException` will be thrown.
 
 See: link:https://github.com/apache/tinkerpop/tree/x.y.z/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/AsDateStep.java[source],
@@ -639,6 +640,7 @@ list of string instead.
 Null values from the incoming traverser are not processed and remain as null when returned.
 
 *Exceptions*
+
 None
 
 See: link:https://github.com/apache/tinkerpop/tree/x.y.z/gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/AsStringGlobalStep.java[source],
@@ -1063,6 +1065,7 @@ The `global` scope will operate on individual string traverser. The `local` scop
 Null values from the incoming traverser are not processed and remain as null when returned.
 
 *Exceptions*
+
 * For `Scope.global` or parameterless function calls, if the incoming traverser is a non-String value then an `IllegalArgumentException` will be thrown.
 * For `Scope.local`, if the incoming traverser is not a string or a list of strings then an `IllegalArgumentException` will be thrown.
 
@@ -1161,6 +1164,7 @@ The `global` scope will operate on individual string traverser. The `local` scop
 Null values from the incoming traverser are not processed and remain as null when returned.
 
 *Exceptions*
+
 * For `Scope.global` or parameterless function calls, if the incoming traverser is a non-String value then an `IllegalArgumentException` will be thrown.
 * For `Scope.local`, if the incoming traverser is not a string or a list of strings then an `IllegalArgumentException` will be thrown.
 
@@ -1478,6 +1482,7 @@ The `global` scope will operate on individual string traverser. The `local` scop
 Null values from the incoming traverser are not processed and remain as null when returned.
 
 *Exceptions*
+
 * For `Scope.global` or parameterless function calls, if the incoming traverser is a non-String value then an `IllegalArgumentException` will be thrown.
 * For `Scope.local`, if the incoming traverser is not a string or a list of strings then an `IllegalArgumentException` will be thrown.
 
@@ -1534,6 +1539,7 @@ The `global` scope will operate on individual string traverser. The `local` scop
 Null values from the incoming traverser are not processed and remain as null when returned.
 
 *Exceptions*
+
 * For `Scope.global` or parameterless function calls, if the incoming traverser is a non-String value then an `IllegalArgumentException` will be thrown.
 * For `Scope.local`, if the incoming traverser is not a string or a list of strings then an `IllegalArgumentException` will be thrown.
 
@@ -1564,6 +1570,7 @@ The `global` scope will operate on individual string traverser. The `local` scop
 Null values from the incoming traverser are not processed and remain as null when returned.
 
 *Exceptions*
+
 * For `Scope.global` or parameterless function calls, if the incoming traverser is a non-String value then an `IllegalArgumentException` will be thrown.
 * For `Scope.local`, if the incoming traverser is not a string or a list of strings then an `IllegalArgumentException` will be thrown.
 
@@ -1596,6 +1603,7 @@ The `global` scope will operate on individual string traverser. The `local` scop
 Null values from the incoming traverser are not processed and remain as null when returned.
 
 *Exceptions*
+
 * For `Scope.global` or parameterless function calls, if the incoming traverser is a non-String value then an `IllegalArgumentException` will be thrown.
 * For `Scope.local`, if the incoming traverser is not a string or a list of strings then an `IllegalArgumentException` will be thrown.
 
@@ -1625,6 +1633,7 @@ The `global` scope will operate on individual string traverser. The `local` scop
 Null values from the incoming traverser are not processed and remain as null when returned.
 
 *Exceptions*
+
 * For `Scope.global` or parameterless function calls, if the incoming traverser is a non-String value then an `IllegalArgumentException` will be thrown.
 * For `Scope.local`, if the incoming traverser is not a string or a list of strings then an `IllegalArgumentException` will be thrown.
 
@@ -1654,6 +1663,7 @@ The `global` scope will operate on individual string traverser. The `local` scop
 Null values from the incoming traverser are not processed and remain as null when returned.
 
 *Exceptions*
+
 * For `Scope.global` or parameterless function calls, if the incoming traverser is a non-String value then an `IllegalArgumentException` will be thrown.
 * For `Scope.local`, if the incoming traverser is not a string or a list of strings then an `IllegalArgumentException` will be thrown.
 
@@ -1682,6 +1692,7 @@ The `global` scope will operate on individual string traverser. The `local` scop
 Null values from the incoming traverser are not processed and remain as null when returned.
 
 *Exceptions*
+
 * For `Scope.global` or parameterless function calls, if the incoming traverser is a non-String value then an `IllegalArgumentException` will be thrown.
 * For `Scope.local`, if the incoming traverser is not a string or a list of strings then an `IllegalArgumentException` will be thrown.
 

gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/DateDiffStep.java

@@ -55,7 +55,7 @@ protected Long map(final Traverser.Admin<S> traverser) {
 
         if (!(object instanceof Date))
             throw new IllegalArgumentException(
-                    String.format("DateDiff can only take Date as argument, encountered %s", object.getClass()));
+                    String.format("DateDiff can only take Date as argument, encountered %s", object == null ? null : object.getClass()));
 
         final Date otherDate = value != null ? value :
                 dateTraversal != null ? TraversalUtil.apply(traverser, dateTraversal) : null;

gremlin-core/src/test/java/org/apache/tinkerpop/gremlin/process/traversal/step/map/DateDiffStepTest.java

@@ -96,4 +96,9 @@ public void shouldHandleNullDate() {
     public void shouldThrowWhenInputIsNotDate() {
         __.__("2023-08-23T00:00:00Z").dateDiff(new Date()).next();
     }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void shouldThrowWhenInputIsNull() {
+        __.__((Object) null).dateDiff(new Date()).next();
+    }
 }