Parser crashes with TypeError when visiting contract parts

Solhint crashes with a TypeError: Cannot read properties of null (reading 'accept') when attempting to parse Solidity files. The error occurs during AST building when visiting contract parts ### Steps to Reproduce I experienced this error when I ran solhint on https://github.com/paritytech/polkadot-sdk *Run solhint with the following command: `solhint ./**/*.sol -c solhint.json -f json --disc` The parser crashes before completing the scan ### Error Output ``` [solhint] Warning: Rule 'custom-errors' doesn't exist [solhint] Warning: Rule 'contract-name-camelcase' doesn't exist [solhint] Warning: Rule 'event-name-camelcase' doesn't exist [solhint] Warning: Rule 'named-return-values' doesn't exist TypeError: Cannot read properties of null (reading 'accept') at ASTBuilder.visit (/opt/homebrew/lib/node_modules/solhint/node_modules/@solidity-parser/parser/dist/index.cjs.js:3236:19) at ASTBuilder.visitContractPart (/opt/homebrew/lib/node_modules/solhint/node_modules/@solidity-parser/parser/dist/index.cjs.js:38463:17) at ContractPartContext.accept (/opt/homebrew/lib/node_modules/solhint/node_modules/@solidity-parser/parser/dist/index.cjs.js:35068:22) at ASTBuilder.visit (/opt/homebrew/lib/node_modules/solhint/node_modules/@solidity-parser/parser/dist/index.cjs.js:3236:19) at /opt/homebrew/lib/node_modules/solhint/node_modules/@solidity-parser/parser/dist/index.cjs.js:38477:58 at Array.map (<anonymous>) at ASTBuilder.visitContractDefinition (/opt/homebrew/lib/node_modules/solhint/node_modules/@solidity-parser/parser/dist/index.cjs.js:38477:41) at ContractDefinitionContext.accept (/opt/homebrew/lib/node_modules/solhint/node_modules/@solidity-parser/parser/dist/index.cjs.js:34951:22) at ASTBuilder.visit (/opt/homebrew/lib/node_modules/solhint/node_modules/@solidity-parser/parser/dist/index.cjs.js:3236:19) at /opt/homebrew/lib/node_modules/solhint/node_modules/@solidity-parser/parser/dist/index.cjs.js:38456:59 ``` The error occurs in the `@solidity-parser/parser` dependency when building the AST. The parser encounters a null node when attempting to visit contract parts, suggesting it may be related to: * Incomplete or malformed contract syntax * Unsupported Solidity language features * Edge cases in the parser's handling of certain contract structures