Return null instead of an empty string when no error was found

src/converter/dimacs/LogicalExpressionValidator.ts

@@ -23,17 +23,17 @@ export class LogicalExpressionValidator {
   /**
    * Validates a logical expression
    * @param logicalExpression {string} logical expression
-   * @returns {string[]} an array of errors. If empty, the logical expression is valid.
+   * @returns {string[]} an array of errors, or null if there are none.
    */
-  public validateLogicalExpression(logicalExpression: string): string[] {
+  public validateLogicalExpression(logicalExpression: string): string[] | null {
     let tokens = this.lex.tokenize(logicalExpression);
     if (tokens.length == 0) return [];
 
     //Verify formula integrity
     return this.verifyTokens(tokens);
   }
 
-  private verifyTokens(tokens: Token[]): string[] {
+  private verifyTokens(tokens: Token[]): string[] | null {
     let errors: string[] = [];
     let wasOperator = false;
     let wasVariable = false;
@@ -107,6 +107,10 @@ export class LogicalExpressionValidator {
       wasNegate = token.name == TokenName.negate;
     }
 
-    return errors;
+    if (errors.length > 0) {
+      return errors;
+    } else {
+      return null;
+    }
   }
 }

src/pages/solve/SAT.tsx

@@ -50,7 +50,7 @@ const SAT: NextPage = () => {
             value.toString()
           );
 
-          if (errors.length > 0) {
+          if (errors) {
             setErrorString(errors.toString());
           } else {
             setErrorString("");