[plsql] Fix for #2225 -- rename EMPTY to EMPTY_ to remove symbol conflict (#3655)

* Fix for #2225

* Fix warning messages from C# compiler.

* Add in changes from master into this branch

(Couldn't get github fast forward, nor github pr to work.)

Author: kaby76

sql/plsql/CSharp/PlSqlLexerBase.cs

@@ -3,7 +3,6 @@
 using System.Reflection;
 using Antlr4.Runtime;
 using Antlr4.Runtime.Misc;
-using Antlr4.Runtime;
 
 public class PlSqlLexerBase : Lexer
 {

sql/plsql/CSharp/PlSqlParserBase.cs

@@ -1,10 +1,8 @@
-using Antlr4.Runtime;
 using System;
 using System.IO;
 using System.Reflection;
 using Antlr4.Runtime;
 using Antlr4.Runtime.Misc;
-using Antlr4.Runtime;
 
 public abstract class PlSqlParserBase : Parser
 {

sql/plsql/PlSqlLexer.g4

@@ -485,7 +485,7 @@ ELSIF:                        'ELSIF';
 EM:                           'EM';
 EMPTY_BLOB:                   'EMPTY_BLOB';
 EMPTY_CLOB:                   'EMPTY_CLOB';
-EMPTY:                        'EMPTY';
+EMPTY_:                        'EMPTY';
 ENABLE_ALL:                   'ENABLE_ALL';
 ENABLE:                       'ENABLE';
 ENABLE_PARALLEL_DML:          'ENABLE_PARALLEL_DML';

sql/plsql/PlSqlParser.g4

@@ -6084,7 +6084,7 @@ unary_logical_expression
 logical_operation:
     ( NULL_
     | NAN | PRESENT
-    | INFINITE | A_LETTER SET | EMPTY
+    | INFINITE | A_LETTER SET | EMPTY_
     | OF TYPE? '(' ONLY? type_spec (',' type_spec)* ')'
     )
     ;
@@ -6244,9 +6244,9 @@ json_function
     | JSON_OBJECT '(' json_object_content ')'
     | JSON_OBJECTAGG '(' KEY? expression VALUE expression ((NULL_ | ABSENT) ON NULL_)? (RETURNING ( VARCHAR2 ('(' UNSIGNED_INTEGER ( BYTE | CHAR )? ')')? | CLOB | BLOB ))?  STRICT? (WITH UNIQUE KEYS)?')'
     | JSON_QUERY '(' expression (FORMAT JSON)? ',' CHAR_STRING json_query_returning_clause json_query_wrapper_clause? json_query_on_error_clause? json_query_on_empty_clause? ')'
-    | JSON_SERIALIZE '(' CHAR_STRING (RETURNING json_query_return_type)? PRETTY? ASCII? TRUNCATE? ((NULL_ | ERROR | EMPTY (ARRAY | OBJECT)) ON ERROR)? ')'
+    | JSON_SERIALIZE '(' CHAR_STRING (RETURNING json_query_return_type)? PRETTY? ASCII? TRUNCATE? ((NULL_ | ERROR | EMPTY_ (ARRAY | OBJECT)) ON ERROR)? ')'
     | JSON_TRANSFORM '(' expression ',' json_transform_op (',' json_transform_op)* ')'
-    | JSON_VALUE '('  expression (FORMAT JSON)? (',' CHAR_STRING? json_value_return_clause? ((ERROR | NULL_ | DEFAULT literal)? ON ERROR)? ((ERROR | NULL_ | DEFAULT literal)? ON EMPTY)? json_value_on_mismatch_clause?')')?
+    | JSON_VALUE '('  expression (FORMAT JSON)? (',' CHAR_STRING? json_value_return_clause? ((ERROR | NULL_ | DEFAULT literal)? ON ERROR)? ((ERROR | NULL_ | DEFAULT literal)? ON EMPTY_)? json_value_on_mismatch_clause?')')?
     ;
 
 json_object_content
@@ -6260,7 +6260,7 @@ json_object_entry
     ;
 
 json_table_clause
-    : JSON_TABLE '(' expression (FORMAT JSON)? (',' CHAR_STRING)? ((ERROR | NULL_) ON ERROR)? ((EMPTY | NULL_) ON EMPTY)? json_column_clause? ')'
+    : JSON_TABLE '(' expression (FORMAT JSON)? (',' CHAR_STRING)? ((ERROR | NULL_) ON ERROR)? ((EMPTY_ | NULL_) ON EMPTY_)? json_column_clause? ')'
     ;
 
 json_array_element
@@ -6308,11 +6308,11 @@ json_query_wrapper_clause
     ;
 
 json_query_on_error_clause
-    : (ERROR | NULL_ | EMPTY | EMPTY ARRAY | EMPTY OBJECT)? ON ERROR
+    : (ERROR | NULL_ | EMPTY_ | EMPTY_ ARRAY | EMPTY_ OBJECT)? ON ERROR
     ;
 
 json_query_on_empty_clause
-    : (ERROR | NULL_ | EMPTY | EMPTY ARRAY | EMPTY OBJECT)? ON EMPTY
+    : (ERROR | NULL_ | EMPTY_ | EMPTY_ ARRAY | EMPTY_ OBJECT)? ON EMPTY_
     ;
 
 json_value_return_clause
@@ -6394,7 +6394,7 @@ other_function
     | XMLPI
       '(' (NAME identifier | EVALNAME concatenation) (',' concatenation)? ')' ('.' general_element_part)*
     | XMLQUERY
-      '(' concatenation xml_passing_clause? RETURNING CONTENT (NULL_ ON EMPTY)? ')' ('.' general_element_part)*
+      '(' concatenation xml_passing_clause? RETURNING CONTENT (NULL_ ON EMPTY_)? ')' ('.' general_element_part)*
     | XMLROOT
       '(' concatenation (',' xmlroot_param_version_part)? (',' xmlroot_param_standalone_part)? ')' ('.' general_element_part)*
     | XMLSERIALIZE
@@ -7884,7 +7884,7 @@ non_reserved_keywords_pre12c
     | ELIMINATE_OUTER_JOIN
     | EMPTY_BLOB
     | EMPTY_CLOB
-    | EMPTY
+    | EMPTY_
     | ENABLE
     | ENABLE_PRESET
     | ENCODING