Everywhere: Use default StringView constructor over nullptr

While null StringViews are just as bad, these prevent the removal of
StringView(char const*) as that constructor accepts a nullptr.

No functional changes.

Userland/Libraries/LibRegex/RegexByteCode.cpp

@@ -855,7 +855,7 @@ Vector<String> OpCode_Compare::variable_arguments_to_string(Optional<MatchInput>
     Vector<String> result;
 
     size_t offset { state().instruction_position + 3 };
-    RegexStringView view = ((input.has_value()) ? input.value().view : nullptr);
+    RegexStringView view = ((input.has_value()) ? input.value().view : StringView {});
 
     for (size_t i = 0; i < arguments_count(); ++i) {
         auto compare_type = (CharacterCompareType)m_bytecode->at(offset++);

Userland/Libraries/LibRegex/RegexLexer.cpp

@@ -32,7 +32,7 @@ char const* Token::name() const
 }
 
 Lexer::Lexer()
-    : GenericLexer(StringView { nullptr })
+    : GenericLexer(StringView {})
 {
 }
 
@@ -62,7 +62,7 @@ char Lexer::consume()
 void Lexer::reset()
 {
     m_index = 0;
-    m_current_token = { TokenType::Eof, 0, StringView(nullptr) };
+    m_current_token = { TokenType::Eof, 0, {} };
     m_previous_position = 0;
 }
 
@@ -178,7 +178,7 @@ Token Lexer::next()
         return emit_token(TokenType::Char);
     }
 
-    return Token(TokenType::Eof, m_index, nullptr);
+    return Token(TokenType::Eof, m_index, {});
 }
 
 }

Userland/Libraries/LibRegex/RegexLexer.h

@@ -61,7 +61,7 @@ public:
 private:
     TokenType m_type { TokenType::Eof };
     size_t m_position { 0 };
-    StringView m_value { nullptr };
+    StringView m_value {};
 };
 
 class Lexer : public GenericLexer {
@@ -77,7 +77,7 @@ public:
 
 private:
     size_t m_previous_position { 0 };
-    Token m_current_token { TokenType::Eof, 0, StringView(nullptr) };
+    Token m_current_token { TokenType::Eof, 0, {} };
 };
 
 }

Userland/Libraries/LibRegex/RegexParser.cpp

@@ -169,7 +169,7 @@ ALWAYS_INLINE void Parser::reset()
     m_parser_state.lexer.reset();
     m_parser_state.current_token = m_parser_state.lexer.next();
     m_parser_state.error = Error::NoError;
-    m_parser_state.error_token = { TokenType::Eof, 0, StringView(nullptr) };
+    m_parser_state.error_token = { TokenType::Eof, 0, {} };
     m_parser_state.capture_group_minimum_lengths.clear();
     m_parser_state.capture_groups_count = 0;
     m_parser_state.named_capture_groups_count = 0;

Userland/Libraries/LibRegex/RegexParser.h

@@ -101,7 +101,7 @@ protected:
         Lexer& lexer;
         Token current_token;
         Error error = Error::NoError;
-        Token error_token { TokenType::Eof, 0, StringView(nullptr) };
+        Token error_token { TokenType::Eof, 0, {} };
         ByteCode bytecode;
         size_t capture_groups_count { 0 };
         size_t named_capture_groups_count { 0 };