Fix syntax tree issue

Author: GrahamTheCoder

CodeConverter/CSharp/VisualBasicEqualityComparison.cs

@@ -154,7 +154,7 @@ public bool TryConvertToNullOrEmptyCheck(VBSyntax.BinaryExpressionSyntax node, E
                 var arg = lhsEmpty ? rhs : lhs;
                 var nullOrEmpty = SyntaxFactory.InvocationExpression(
                     SyntaxFactory.MemberAccessExpression(SyntaxKind.SimpleMemberAccessExpression,
-                        SyntaxFactory.IdentifierName("string"),
+                        SyntaxFactory.PredefinedType(SyntaxFactory.Token(SyntaxKind.StringKeyword)),
                         SyntaxFactory.IdentifierName("IsNullOrEmpty")),
                     SyntaxFactory.ArgumentList(SyntaxFactory.SeparatedList(new[]
                         {SyntaxFactory.Argument(arg)})));

Tests/CSharp/ExpressionTests/BinaryExpressionTests.cs

@@ -196,9 +196,7 @@ private void TestMethod(string str)
     {
         int result = 5 - (string.IsNullOrEmpty(str) ? 1 : 2);
     }
-}
-1 target compilation errors:
-CS0103: The name 'string' does not exist in the current context");
+}");
         }
     }
 }

Tests/CSharp/ExpressionTests/ExpressionTests.cs

@@ -691,9 +691,7 @@ private void TestMethod(string str)
     {
         bool result = string.IsNullOrEmpty(str) ? true : false;
     }
-}
-1 target compilation errors:
-CS0103: The name 'string' does not exist in the current context");
+}");
         }
 
         [Fact]
@@ -730,9 +728,7 @@ private void TestMethod(string str)
     {
         bool result = !(string.IsNullOrEmpty(str) ? true : false);
     }
-}
-1 target compilation errors:
-CS0103: The name 'string' does not exist in the current context");
+}");
         }
 
         [Fact]

Tests/CSharp/ExpressionTests/StringExpressionTests.cs

@@ -146,9 +146,7 @@ public void Foo()
             // 
         }
     }
-}
-1 target compilation errors:
-CS0103: The name 'string' does not exist in the current context");
+}");
         }
 
         [Fact]
@@ -209,9 +207,7 @@ public void Foo()
             // 
         }
     }
-}
-1 target compilation errors:
-CS0103: The name 'string' does not exist in the current context");
+}");
         }
 
         [Fact]

Tests/CSharp/MemberTests/PropertyMemberTests.cs

@@ -487,9 +487,7 @@ public string Y
             }
         }
     }
-}
-1 target compilation errors:
-CS0103: The name 'string' does not exist in the current context");
+}");
         }
 
         [Fact]

Tests/CSharp/StatementTests/StatementTests.cs

@@ -1368,9 +1368,7 @@ public static int FindTextInCol(string w, int pTitleRow, int startCol, string ne
 
         return -1;
     }
-}
-1 target compilation errors:
-CS0103: The name 'string' does not exist in the current context");
+}");
         }
 
         [Fact]