I got the same empty response, even after adding the &version=4.12:
http://developer.echonest.com/api/v4/song/identify?api_key=GW2XBLB17GM7A8WS2&code=eJy1mFGSJCkORK8EEgg4DiC4_xH2QZlN7rZtkR9t89FulUEECOTuEh1CiCM8IJUXlPSC2l9w_v0O0x8Qy37BWg-QUF4Q-ws0viD7C5Y-IIT8gjP973Cm_x3eWRj2gHhm_x10vsDqC1p-wYwveOf3EPN3KPqAL1l4K0XlBXm9oI4XXIL8BjHsF3zJUXvB-5zfSvmShfSAb1mYL3grJaUXfFFKecA3pYwXfFFKekGfL1j7AV_86mz6dzg2_DsseQCn_YK_ye_bCVt4wZwP-DuVPfPbxwP-SmV_lYW31_1NFuILVnrAlyx8OeenUqa8wOsL_qoevZzwi8p2e8C_6KJfatm_5qLvavWlo9AXfMlgfcFfZDAEe8GXWvbszN8afGbhX-w33n37lwy-FPrKgmYRNc3uWprOleaOY0WXkVWqLxsqOXY3LTM0qNRt9Ji6Rg_eVsuxLQ_3ldWG9hiXpp1GaKtWrVo8z9ykaeWPZrkXCSlL0tBU4-CzsUpvYUoXsx09-YojldGkB4uzq_PRSt1UvYw5Rimxa5OZZEtn70VSbK1pD9Kj-CoM7K695Bu9-Z6xNnONPTb1JbZshVWq0V9E7bZrkcpSonpj9tTibm62cp38ZdH5WipKijHfDbaZ02o1Tyll5LC4H60ZJZn0YSPPKnsIZ_kBU4_5j2cf2LHVVEqXrJb23s6DFnrqY-2Yz4Vx31FcYnWbzis8GSyyzUfTNlWlm6e9FiStd5S-Lef72Z3vTsWRtLW2cyTRer3z5eF4NTnoJtDpjsYVdIc0jLMtW_l8z09UbMeL93TCCnneUZUW5BPzZ0f_L-Y7eue7Md-o7ugI8OwT843qE_ONaq8S6435LtTSCvCNvJSUe75Rla7LbyyRPYwP3Jn_ePaBSf4lRmkipeU8hnJgpTWbeTSIMXIWl9Dq0slZxc16pNXysklVOQchu7gd9sP6mqYkHicIJ4Odn1Ho2Rjxbc2Koh9Vdlp4LU-XO4pxxn5HI_dMuzNXgWpp7LpHXcWSFiVm6by9xs98d7XP6B7FtteuOafe6g2jpL6miECQM3pXuwvd0cBplzva--rjs-7d_h_r_oz-tu7d6h29M7vXsT9w1_3j2QcgSMIWJMq0LjvB6IUCMlz2lRVhRjaGh8y1U94pcvpt7M56mFRekG3N3afWKjoda12Zz5Y28hKQ6FxQQEhc2mPL2rstrs6QZWkXzxrqbEyAiCy0Ye6woU5b0CdpzRTyGNV4oSrR3NHSziGeIJ1gdfQ20kw7qutOislQ0Opu3SsvuFjJocL03bY3xGQ-rRFyGSkXlF5K8BJE6mieCvusBYKhUcOAds94TenHKhrHw0PD904YywIMPu6IKibaX1yR-7FNLDkXrM3IlLBU1HADWlNLn1aQVpxZdiwcT1AmyTGxPv3fjTmUjDwcP9_YMITlkAvH9TMBZ0HO_wHqRGt_PPuv0YCQHd83QscSlXPbPcE6qdV3hkpbUA9ONG2UqPj92tY3xyUwjHo4xsIgKFjMWKYYySPze9aA2XO0zjQis3dsaVNpekL1OYyaUqcQY-dUIjJvbrQL7VSRYS3jmMspOHWLh17xFUOUrF9upPH8z93gB4VjZ0xoFmx-iBel_NxYTj39GVWKYWkUyhprisUhqN8w8GuKTbVuJVmqbcFaJBdW26Od9nM59kj6eDukLXApQUhC3-3OvCjYPzNTxBDC2Tka5ZS4i8kH2AYn8L_PPlAKiWs9dBx_ktTzCCvYI85Dj-09TvxsU5htmCg2A6_DxrbbghR7BlUb6BUvIKfLZ_I50sqrw_-6Fx0A6szBDr_qNgtDl_WeE-SSODcdIqI1oqEGUwa1CMkPdWFXpwkZlAzHsrCEetISPCHWPrBkH9IgeQ-z0MDUCB8RvMSgyKPLbLCFVi-uGufCv-LPfgU6HJdpHYNhIaol0GXQa4Qrp58Icrr20qipafPb2uzF_ZwHLuARuReh5qaErgfyawieFgfCoSB-9yVOJ0Onk-JxNckdzWRH8DEs5O40OpF8n8llQH38n-ENTY_DcL2l9NgcnTO2bFtThL6Z5f8BPlz6x7MPUD0DxsJ0QrroXAckOq1UoZuROitMxAQ4v-h7zUldwG17Gur5fnFf7sgNaoxjbQYHaKv2z3woqSDQUoX42ykQlPWYaIIobHnXywNePqNkbnKgoR5folh3JD9GayVs-C0U_hzrGu2GRrWlJ8CG_b53Z5nhnF7cp4QyvUCs-YnqSHCmekzO2OedAJ7EEIVTR-NUoWYJJw1AN8uBRHFnpuGDhLQMZ5ckFUvtdgo_m3Gqv96o7pJ3vz3RSCJxO1TDRc-3esP9J1Jqv9oHNNAr__HsA6WirEVjRYuJvXZagE0XrYajYUvwDCctJtTDHKA80qmauA3UYsgPn6Otcjq_hOshztlRxaQdyZbCOsUg0tlQq3ztfBrrcbpfKi_motaEmHFTRFlgJOkrow86qDOK4046XCrIoNrQYm_ZmbqdaRCI6ARENupPQGPRK9-oTt30iKTmjSCTM4Q4rWZEeIQ5Ss1cWDAt1qS-YG6GFdJRx2iUG9-Ob5_LSNbJrSSdrdFt49NCKR8IKRbasHOnqB_42cL_PvvAfwA_QWwD&version=4.12
Would be nice to have a hint why the server respons with 'success' even if songs[] is empty.