fix functions to accept null

Author: SteveL-MSFT

dsc_lib/src/functions/coalesce.rs

@@ -22,20 +22,23 @@ impl Function for Coalesce {
             accepted_arg_ordered_types: vec![vec![
                 FunctionArgKind::Array,
                 FunctionArgKind::Boolean,
+                FunctionArgKind::Null,
                 FunctionArgKind::Number,
                 FunctionArgKind::Object,
                 FunctionArgKind::String,
             ]],
             remaining_arg_accepted_types: Some(vec![
                 FunctionArgKind::Array,
                 FunctionArgKind::Boolean,
+                FunctionArgKind::Null,
                 FunctionArgKind::Number,
                 FunctionArgKind::Object,
                 FunctionArgKind::String,
             ]),
             return_types: vec![
                 FunctionArgKind::Array,
                 FunctionArgKind::Boolean,
+                FunctionArgKind::Null,
                 FunctionArgKind::Number,
                 FunctionArgKind::Object,
                 FunctionArgKind::String,

dsc_lib/src/functions/create_object.rs

@@ -22,6 +22,7 @@ impl Function for CreateObject {
             accepted_arg_ordered_types: vec![],
             remaining_arg_accepted_types: Some(vec![
                 FunctionArgKind::String,
+                FunctionArgKind::Null,
                 FunctionArgKind::Number,
                 FunctionArgKind::Boolean,
                 FunctionArgKind::Object,